Capacitance type sensor

ABSTRACT

A capacitance type gyro sensor includes a semiconductor substrate, a first electrode integrally including a first base portion and first comb tooth portions and a second electrode integrally including a second base portion and second comb tooth portions, formed by processing the surface portion of the semiconductor substrate. The first electrode has first drive portions that extend from opposed portions opposed to the respective second comb tooth portions on the first base portion toward the respective second comb tooth portions. The second electrode has second drive portions formed on the tip end portions of the respective second comb tooth portions opposed to the respective first drive portions. The first drive portions and the second drive portions engage with each other at an interval like comb teeth.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 13/274,292,filed on Oct. 14, 2011. Furthermore, this application claims the benefitof priority of Japanese applications 2010-212341 filed on Sep. 22, 2010,2010-232910 filed on Oct. 15, 2010, 2010-271982 filed on Dec. 6, 2010,2010-277213 filed on Dec. 13, 2010, and 2010-277214 filed on Dec. 13,2010. The disclosures of these prior U.S. and Japanese applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a MEMS sensor and a method formanufacturing the same, and a MEMS package with the MEMS sensor.

2. Description of Related Arts

A MEMS (Micro Electro Mechanical Systems) sensor detects acceleration,an angular velocity, and a pressure, etc., applied to an object by usinga “structure” that changes according to application of an externalforce.

As a detection method of a MEMS sensor, for example, a capacitance typethat performs detection based on a change in capacitance of a capacitoris known. As detailed devices, capacitance type gyro sensors andcapacitance type acceleration sensors, etc., are known.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a capacitance typegyro sensor that is downsized and has excellent detection sensitivity.

A second object of the present invention is to provide a capacitancetype acceleration sensor that has a simple structure and excellentdetection sensitivity.

A third object of the present invention is to provide a method formanufacturing a MEMS sensor in which a layer for protecting a fixedelectrode and a movable electrode can be formed by a simple method at alow cost, and a MEMS sensor manufactured by this manufacturing method.

A fourth object of the present invention is to provide a highly reliableMEMS package that has a MEMS sensor including a protective layer for afixed electrode and a movable electrode.

A fifth object of the present invention is to provide a MEMS sensor inwhich a lower electrode can be easily formed directly below an upperelectrode via a cavity, the upper electrode and the lower electrode areprevented from being short-circuited by each other, and the detectionaccuracy of the sensor can be improved, and a method for manufacturingthe same.

A sixth object of the present invention is to provide a MEMS packagewith a MEMS sensor having excellent detection accuracy.

A seventh object of the present invention is to provide a MEMS sensor inwhich the variation in size of a first electrode and a second electrodethat have comb-tooth-like shapes and engage with each other can bereduced and the detection accuracy of the sensor can be improved, and amethod for manufacturing the same.

The above-described or other objects, features, and effects of thepresent invention will be clarified by the following description ofpreferred embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a gyro sensor according to a firstpreferred embodiment of the present invention.

FIG. 2 is a schematic plan view of a sensor portion shown in FIG. 1.

FIG. 3 is a plan view of a principal portion of an X-axis sensor shownin FIG. 2.

FIG. 4 is a sectional view of the principal portion of the X-axis sensorshown in FIG. 2, illustrating a section taken along the cutting planeA-A in FIG. 3.

FIG. 5 is a plan view of a principal portion of a Z-axis sensor shown inFIG. 2.

FIG. 6 is a sectional view of the principal portion of the Z-axis sensorshown in FIG. 2, illustrating a section taken along the cutting planeB-B in FIG. 5.

FIG. 7A to FIG. 7G are sectional views showing parts of a manufacturingprocess of the gyro sensor according to the first preferred embodimentof the present invention in order of steps.

FIG. 8 is a view showing an exemplary variation of first drive portionsand second drive portions shown in FIG. 5.

FIG. 9 is a schematic plan view of an acceleration sensor according to asecond preferred embodiment of the present invention.

FIG. 10 is a schematic plan view of a sensor portion shown in FIG. 9.

FIG. 11 is a plan view of a principal portion of an X-axis sensor shownin FIG. 10.

FIG. 12 is a sectional view of the principal portion of the X-axissensor shown in FIG. 10, illustrating a section taken along the cuttingplane C-C in FIG. 11.

FIG. 13 is a plan view of a principal portion of a Z-axis sensor shownin FIG. 10.

FIG. 14 is a sectional view of the principal portion of the Z-axissensor shown in FIG. 10, illustrating a section taken along the cuttingplane D-D in FIG. 13.

FIG. 15A to FIG. 15G are sectional views showing parts of amanufacturing process of the acceleration sensor according to the secondpreferred embodiment of the present invention in order of steps.

FIG. 16 is a view showing an exemplary variation of a Z movableelectrode shown in FIG. 14.

FIG. 17 is a view showing an exemplary variation of dielectric layersshown in FIG. 14.

FIG. 18 is a view showing an exemplary variation of the dielectriclayers shown in FIG. 16.

FIG. 19 is a schematic perspective view of a MEMS package according to athird preferred embodiment of the present invention.

FIG. 20 is a sectional view of a principal portion of the MEMS packageshown in FIG. 19, illustrating a section taken along the cutting planeE-E in FIG. 19.

FIG. 21 is a schematic plan view of an acceleration sensor shown in FIG.19.

FIG. 22 is a plan view of a principal portion of an X-axis sensor shownin FIG. 21.

FIG. 23 is a sectional view of the principal portion of the X-axissensor shown in FIG. 21, illustrating a section taken along the cuttingplane F-F in FIG. 22.

FIG. 24 is a plan view of a principal portion of a Z-axis sensor shownin FIG. 21.

FIG. 25 is a sectional view of the principal portion of the Z-axissensor shown in FIG. 21, illustrating a section taken along the cuttingplane G-G in FIG. 24.

FIG. 26A to FIG. 26M are sectional views showing parts of amanufacturing process of the Z-axis sensors shown in FIG. 21 in order ofsteps.

FIG. 27 is a plan view showing a mode in which the Z-axis sensor shownin FIG. 24 is used as an angular velocity sensor.

FIG. 28 is a schematic perspective view of a MEMS package according to afourth preferred embodiment of the present invention.

FIG. 29 is a schematic sectional view of the Z-axis sensor shown in FIG.1.

FIG. 30A to FIG. 30L are sectional views showing parts of amanufacturing process of the Z-axis sensors shown in FIG. 29 in order ofsteps.

FIG. 31 is a plan view showing a mode in which the Z-axis sensor shownin FIG. 29 is used as an acceleration sensor.

FIG. 32 is a view showing an exemplary variation of the Z-axis sensorshown in FIG. 29.

FIG. 33 is a schematic perspective view of a MEMS package according to afifth preferred embodiment of the present invention.

FIG. 34 is a schematic plan view of the angular velocity sensor shown inFIG. 1.

FIG. 35 is a plan view of a principal portion of the X-axis sensor shownin FIG. 2.

FIG. 36 is a sectional view of the principal portion of the X-axissensor shown in FIG. 2, illustrating a section taken along the cuttingplane H-H in FIG. 35.

FIG. 37 is a plan view of a principal portion of the Z-axis sensor shownin FIG. 34.

FIG. 38 is a sectional view of the principal portion of the Z-axissensor shown in FIG. 34, illustrating a section taken along the cuttingplane I-I shown in FIG. 37.

FIG. 39A to FIG. 39K are sectional views showing parts of amanufacturing process of the Z-axis sensors shown in FIG. 34 in order ofsteps.

FIG. 40 is a plan view showing a mode in which the Z-axis sensor shownin FIG. 37 is used as an acceleration sensor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A capacitance type gyro sensor according to an aspect of the presentinvention includes a semiconductor substrate having a cavity inside byforming an upper wall and a bottom wall, and having a surface portionforming the upper wall of the cavity and a back surface portion formingthe bottom wall, a first electrode formed by processing the surfaceportion of the semiconductor substrate, and integrally having a firstbase portion and first comb tooth portions extending from the first baseportion and aligned at intervals like comb teeth, and a second electrodeformed by processing the surface portion of the semiconductor substrate,and integrally having a second base portion and second comb toothportions extending from the second base portion toward the portionsbetween the first comb tooth portions and aligned like comb teeth toengage with the first comb tooth portions at an interval, and drives thefirst electrode or the second electrode up and down with respect to theother electrode and detects an angular velocity applied at the time ofthis driving by detecting a change in capacitance between the first combtooth portion and the second comb tooth portion, wherein the firstelectrode includes first drive portions extending from opposed portionsopposed to the second comb tooth portions of the first base portiontoward the second comb tooth portions, and electrically insulated fromother portions of the first base portion, and the second electrodeincludes second drive portions formed on the tip end portions of thesecond comb tooth portions opposed to the first drive portions so as tobe electrically insulated from other portions of the second comb toothportions, and the first drive portions and the second drive portionsengage with each other at an interval like comb teeth.

In the capacitance type gyro sensor according to an aspect of thepresent invention, the first electrode integrally includes a first baseportion and a comb-tooth-like electrode (an assembly of a plurality offirst comb tooth portions) supported on this first base portion. Thefirst comb tooth portions engage with the comb-tooth-like secondelectrode (assembly of the plurality of second comb tooth portions) atan interval. Accordingly, the first comb tooth portions and the secondcomb tooth portions constitute electrodes of a capacitor (detector) whena fixed voltage is applied between the first comb tooth portions and thesecond comb tooth portions and which changes in capacitance due to achange in interval between these and/or a change in opposing area.

On the other hand, on the first base portion of the first electrode,first drive portions extending toward the second comb tooth portionsdisposed between the first comb tooth portions adjacent to each otherare provided. Second drive portions are provided on tip end portions ofthe second comb tooth portions facing the first drive portions, and thefirst drive portions and the second drive portions engage with eachother like comb teeth. Accordingly, the first drive portions and thesecond drive portions drive either the first electrode or the secondelectrode by coulomb forces generated by changes in drive voltages whenthe drive voltages are applied between these electrodes.

In this capacitance type gyro sensor, the first comb tooth portions andthe second comb tooth portions for detecting an angular velocity and thefirst drive portions and the second drive portions for driving the firstelectrode and the second electrode are all formed by processing thesurface portion of the semiconductor substrate. Therefore, the thicknessof the whole sensor is substantially the thickness of the substrate, sothat the sensor can be downsized.

Next, as an example of angular velocity detection by using thiscapacitance type gyro sensor, assuming a three-dimensional orthogonalXYZ coordinate system indicating the thickness direction of thesemiconductor substrate in the Z-axis direction, detection of an angularvelocity applied around the X-axis when the first electrode is driven inthe Z-axis direction will be described.

First, between the first drive portions and the second drive portionsthat engage with each other like comb teeth, drive voltages with thesame polarity and drive voltages with different polarities arealternately applied. Accordingly, between the first drive portions andthe second drive portions, coulomb repulsive and attractive forces arealternately generated. As a result, the first comb tooth portionsintegrated with the first drive portions oscillate (are driven) up anddown (along the thickness direction of the semiconductor substrate)along the Z-axis direction like a pendulum around the second comb toothportions as a center of oscillation. At this time, the first driveportions and the second drive portions as drive electrodes for drivingthe first electrode are disposed to engage with each other like combteeth, so that the opposing area between these can be made larger thanin the case where one drive electrode and the other drive electrode arejust opposed to each other or just adjacent to each other. Therefore,the first electrode can be oscillated with a large amplitude, so thatthe detection sensitivity can be improved.

Then, in this state, when an angular velocity to rotate the firstelectrode around the X axis as a central axis is applied to the firstelectrode being oscillated, a coriolis force is generated to the firstelectrode in the Y-axis direction. This coriolis force changes thedistance between the first comb tooth portions (first electrode) and thesecond comb tooth portions (second electrode) (electrode-to-electrodedistance) and/or the opposing area. Then, by detecting a change incapacitance between the movable electrode and the fixed electrode causedby this change in electrode-to-electrode distance and/or opposing area,the angular velocity around the X-axis can be detected.

The capacitance type gyro sensor according to the present invention mayfurther include first insulating layers that are embedded in the firstbase portion so as to surround the opposed portions and insulate andseparate the opposed portions from other portions of the first baseportion. The capacitance type gyro sensor according to the presentinvention may further include second insulating layers that are embeddedin the base end portion sides relative to the tip end portions of thesecond comb tooth portions and insulate and separate the tip endportions from other portions of the second comb tooth portions.

When the first insulating layers and/or the second insulating layers areembedded in the semiconductor substrate, the surface of thesemiconductor substrate can be efficiently used as a space for leadingwirings to be connected to the first electrode and the second electrode.

In the capacitance type gyro sensor according to the present invention,the semiconductor substrate may be a conductive silicon substrate.

When the semiconductor substrate is a conductive silicon substrate,without applying a special treatment for giving conductivity to thefirst electrode and the second electrode molded to have predeterminedshapes, the molded structures can be used as they are as electrodes.Portions except for the portions to be used as electrodes can be used aswirings.

A capacitance type gyro sensor according to another aspect of thepresent invention includes a semiconductor substrate having a cavityinside by forming an upper wall and a bottom wall, and having a surfaceportion forming the upper wall of the cavity and a back surface portionforming the bottom wall, a first electrode formed by processing thesurface portion of the semiconductor substrate, and integrally having afirst base portion and first comb tooth portions extending from thefirst base portion and aligned at intervals like comb teeth, a secondelectrode formed by processing the surface portion of the semiconductorsubstrate, and integrally having a second base portion and second combtooth portions extending from the second base portion toward theportions between the first comb tooth portions and aligned like combteeth to engage with the first comb tooth portions at an interval, afirst contact wiring that is formed on the surface portion of thesemiconductor substrate and comes into direct contact with the firstelectrode from the surface side, and a second contact wiring that isformed on the surface portion of the semiconductor substrate, and comesinto direct contact with the second electrode from the surface side,wherein the first electrode includes first drive portions extending fromopposed portions opposed to the second comb tooth portions of the firstbase portion toward the second comb tooth portions, and the secondelectrode includes second drive portions formed on the tip end portionsof the second comb tooth portions opposed to the first drive portions soas to be electrically insulated from other portions of the second combtooth portions, and the first drive portions and the second driveportions engage with each other at an interval like comb teeth.

In the capacitance type gyro sensor according to another aspect of thepresent invention, the first drive portions may be electricallyinsulated from other portions of the first base portion, and in thiscase, the capacitance type gyro sensor may further include firstinsulating layers that are embedded in the first base portion so as tosurround the opposed portions and insulate and separate the opposedportions from other portions of the first base portion.

The capacitance type gyro sensor according to another aspect of thepresent invention may further include second insulating layers that areembedded in the base end portion sides relative to the tip end portionsof the second comb tooth portions and insulate and separate the tip endportions from other portions of the second comb tooth portions.

In the capacitance type gyro sensor according to another aspect of thepresent invention, the first contact wiring may include first detectionwiring that comes into contact with the first comb tooth portions, thesecond contact wiring may include second detection wiring that comesinto contact with the base end portion sides relative to the secondinsulating layers of the second comb tooth portions, and the firstelectrode or the second electrode is driven relative to the otherelectrode, and an angular velocity applied at the time of this drivingmay be detected by detecting a change in capacitance between the firstcomb tooth portions and the second comb tooth portions.

In this case, by the first detection wiring and the second detectionwiring, an electric signal corresponding to a change in capacitancecaused by the distance between the first comb tooth portions (firstelectrode) and the second comb tooth portions (second electrode)(electrode-to-electrode distance) and/or the opposing area can bedetected.

A capacitance type acceleration sensor according to an aspect of thepresent invention includes a semiconductor substrate having a cavityinside by forming an upper wall and a bottom wall, and having a surfaceportion forming the upper wall of the cavity and a back surface portionforming the bottom wall, and a first electrode and a second electrodethat are formed by processing the surface portion of the semiconductorsubstrate and have comb-tooth-like shapes to engage with each other atan interval, and detects acceleration when the first electrode or thesecond electrode moves up and down with respect to the other electrodeby detecting a change in capacitance between the first electrode and thesecond electrode, wherein the first electrode includes dielectric layersthat have a predetermined thickness from the surface or the back surfaceto a halfway point of the first electrode along the thickness directionorthogonal to the opposing direction of the second electrode and has apredetermined width along the opposing direction, and conductive layersconsisting of remaining portions except for the dielectric layers.

With the present arrangement, the capacitor for detecting accelerationis formed by making the first electrode and the second electrode opposedto each other. The capacitor detects acceleration based on a change incapacitance caused by oscillation of the first electrode or the secondelectrode.

In this capacitor, the first electrode is partially formed of dielectriclayers having a predetermined thickness along the thickness directionorthogonal to an opposing direction of the first electrode and thesecond electrode and a predetermined width along the opposing direction.

Accordingly, in this capacitor, at a portion in which the dielectriclayer and the second electrode are opposed to each other, theelectrode-to-electrode distance d1 of the capacitor is increased by thewidth W of the dielectric layer as compared with theelectrode-to-electrode distance d2 (distance between the first electrodeand the second electrode) that the capacitor originally has (that is,d1=d2+W). Therefore, a capacitance difference can be provided in onecapacitor.

For example, a method for detecting acceleration when the firstelectrode is a movable electrode that oscillates along the Z-axisdirection and dielectric layers are embedded from the surface to ahalfway point of the movable electrode (first electrode) will bedescribed.

When acceleration in the Z-axis direction is applied to the sensor, thecomb-tooth-like first electrode (movable electrode) oscillates up anddown like a pendulum as a center of oscillation along the Z-axisdirection with respect to the second electrode similarly around thecomb-tooth-like second electrode (fixed electrode).

At this time, when the first electrode oscillates first to the side(upper side) away from the cavity with respect to the second electrode,the capacitance of the capacitor decreases at a decrease rate D1 (D1≧0)based on the electrode-to-electrode distance d1 while the dielectriclayers are opposed to the second electrode. Thereafter, when thedielectric layers completely protrude above the second electrode andonly the conductive layers are opposed to the second electrode, thecapacitance decreases from this timing at a decrease rate D2 (D2≧0)based on the original electrode-to-electrode distance d2. This decreaserate D2 of the capacitance is higher than the decrease rate D1 becausethe electrode-to-electrode distance d2 is smaller than theelectrode-to-electrode distance d1 and the capacitance to decrease perunit time increases. Specifically, when the first electrode starts tooscillate to the upper side, the capacitance of the capacitor decreasesat the first decrease rate D1 and then decreases at the second decreaserate D2 higher than the first decrease rate D1.

On the other hand, when the first electrode oscillates first to the side(the lower side) to approach the cavity with respect to the secondelectrode, until portions of the dielectric layers start to protrude tothe side below the second electrode, the capacitance of the capacitordecreases at the decrease rate D2 based on the electrode-to-electrodedistance d2. Thereafter, when portions of the dielectric layers start toprotrude below the second electrode, the capacitance decreases from thistiming at the decrease rate D1 based on the electrode-to-electrodedistance d1. This decrease rate D1 of the capacitance is smaller thanthe decrease rate D2 because the electrode-to-electrode distance d1 islarger than the electrode-to-electrode distance d2 and the capacitanceto decrease per unit time becomes smaller. Specifically, when the firstelectrode starts to oscillate to the lower side, the capacitance of thecapacitor decreases at the second decrease rate D2 and then decreases atthe first decrease rate D1 smaller than the second decrease rate D2.

Therefore, by detecting whether the capacitance of the capacitordecreases at the relatively small decrease rate D1 and then decreases atthe relatively large decrease rate D2 (D1->D2) or decreases at therelatively large decrease rate D2 and then decreases at the relativelysmall decrease rate D1 (D2->D1), the direction in which the firstelectrode oscillated first (the direction away from the cavity or thedirection approaching the cavity) can be easily grasped. As a result,the direction of the acceleration vector can be accurately detected, sothat the detection sensitivity can be improved.

In addition, this improvement in detection sensitivity is obtained byembedding the dielectric layers in the first electrode constituting thecapacitor, so that the sensor structure can be prevented from becomingcomplicated.

In the capacitance type acceleration sensor according to an aspect ofthe present invention, it is preferable that the dielectric layers areone-sided to one end side in the width direction of the first electrode,and the conductive layer includes a first portion formed adjacently onthe other end side in the width direction to the dielectric layer, and asecond portion formed below the dielectric layer and having a widthlarger than that of the first portion.

With the present arrangement, the conductive layers are formed acrossthe entire region in the thickness direction from the surface to theback surface of the first electrode.

Therefore, for example, when the first electrode is a movable electrodethat oscillates along the Z-axis direction as described above,regardless of the direction of oscillation (upward or downward) of thefirst electrode with respect to the second electrode, the opposing areaof the conductive layer of the first electrode and the second electrodedecreases by necessity. In detail, when the first electrode oscillatesto the upper side first, the opposing area of the first portion of theconductive layer and the second electrode decreases, and on the otherhand, when the first electrode oscillates to the lower side first, theopposing area of the second portion of the conductive layer and thesecond electrode decreases. Specifically, this arrangement shows thecase of D1>0 and D2>0 in the above-described detection method.

Accordingly, a change in capacitance can be detected immediately afterthe first electrode starts to oscillate, so that the magnitude of theacceleration vector immediately after the start of oscillation can alsobe detected.

In the capacitance type acceleration sensor according to an aspect ofthe present invention, it is preferable that the dielectric layers areformed from one end to the other end in the width direction of the firstelectrode and have the same width as that of the first electrode, andthe first electrode has a lamination structure including the dielectriclayers and the conductive layers formed below the dielectric layers.

With the present arrangement, the portion from the surface or the backsurface to a halfway point of the first electrode is entirely formed ofthe dielectric layer. In this case, in the portion in which thedielectric layer and the second electrode are opposed to each other, theconductive layer opposed to the second electrode does not exist, so thatthe capacitance becomes 0 (zero).

Therefore, for example, in the case where the first electrode is amovable electrode that oscillates along the Z-axis direction asdescribed above, when the first electrode oscillates to the upper sidefirst, the capacitance of the capacitor does not change (that is, D1=0)while the dielectric layers are opposed to the second electrode.Thereafter, when the dielectric layers completely protrude above thesecond electrode and only the conductive layers are opposed to thesecond electrode, the capacitance decreases from this timing at thedecrease rate D2 (D2>0) based on the original electrode-to-electrodedistance d2.

On the other hand, when the first electrode oscillates to the lower sidefirst, the capacitance of the capacitor decreases at the decrease rateD2 (D>0) based on the electrode-to-electrode distance d2 until thedielectric layers start to protrude below the second electrode.Thereafter, when the dielectric layers start to protrude below thesecond electrode, the capacitance from this timing does not change (thatis, D1=0).

Therefore, with this arrangement, the direction of the accelerationvector can be judged based on whether the decrease rate of thecapacitance is 0 or not, that is, based on whether or not thecapacitance changes. Therefore, acceleration can be easily detected.

It is also possible that the first electrode is a movable electrode andthe second electrode is a fixed electrode. Alternatively, it is alsopossible that the first electrode is a fixed electrode and the secondelectrode is a movable electrode.

In the capacitance type acceleration sensor according to an aspect ofthe present invention, the semiconductor substrate is preferably aconductive silicon substrate.

When the semiconductor substrate is a conductive silicon substrate, evenwithout applying a special treatment for giving conductivity to thefirst electrode and the second electrode molded to have predeterminedshapes, the molded structures can be used as they are as electrodes. Theportions except for the portions to be used as electrodes can be used aswirings.

A method for manufacturing a MEMS sensor according to an aspect of thepresent invention includes the steps of forming a recess dug to ahalfway point in the thickness direction of a semiconductor substrate byselectively etching the surface layer portion of a sensor region of thesemiconductor substrate having the sensor region and a peripheral regionsurrounding the sensor region, and concurrently, forming comb-tooth-likefixed electrode and movable electrode that engage with each other viathe recess, forming a sacrifice layer that covers the sensor region andexposes the peripheral region, forming a protective layer made of afirst inorganic material on the semiconductor substrate so that theperipheral edge portion of the protective layer is bonded to theperipheral region and the central portion surrounded by the peripheraledge portion covers the sacrifice layer, forming a space between theprotective layer and the sensor region by removing the sacrifice layerdirectly below the protective layer, and forming a cavity by linking thelower portions of the fixed electrode and the movable electrode to eachother by isotropic etching by supplying an etching medium into therecess after removing the sacrifice layer.

According to this method, by forming a layer made of a first inorganicmaterial on the semiconductor substrate in which the fixed electrode andthe movable electrode are formed, even without using a bonding materialsuch as glass frit, the layer for protecting the fixed electrode and themovable electrode can be formed. Therefore, the cost required to formthe protective layer can be reduced.

Concerning workability of formation of the protective layer, theoperation can be made simpler than in the case where a lid substrate isbonded by using a bonding material.

In detail, according to this method, a sacrifice layer is formed tocover the sensor region in which the fixed electrode and the movableelectrode are formed, a protective layer is formed to cover thesacrifice layer, and then, the sacrifice layer directly below theprotective layer is removed. Accordingly, a space is formed in theportion in which the sacrifice layer existed, and a protective layercovering the fixed electrode and the movable electrode is formed on thesensor region via the space. Therefore, without performing an operationsuch as position alignment of wafers, the protective layer can be easilyformed by combining known semiconductor device manufacturing techniques(for example, a CVD (Chemical Vapor Deposition) method, sputtering, andphotolithography, etc.). In addition, when forming the sacrifice layerfor forming the space between the sensor region and the protectivelayer, no cavity is formed directly below the fixed electrode and themovable electrode, and the lower portions of these electrodes are fixedintegrally to the semiconductor substrate. Therefore, even if thesacrifice layer comes into contact with the fixed electrode and themovable electrode, the electrodes do not oscillate due to the impact ofthis contact. Therefore, it is not necessary to add a step forprotecting the electrodes from the sacrifice layer, etc., so that theprocess can be prevented from becoming complicated.

In the method for manufacturing a MEMS sensor according to an aspect ofthe present invention, the step of forming the sacrifice layerpreferably includes a step of forming a first sacrifice layer made of asecond inorganic material different from the material of the protectivelayer so as to close the opening end of the recess formed in the sensorregion, and after forming the first sacrifice layer, a step of forming asecond sacrifice layer made of a metal material on the first sacrificelayer so as to cover the sensor region.

According to this method, the sensor region is covered by the secondsacrifice layer, so that the space between the protective layer and thesensor region is formed by removing (etching) the second sacrificelayer. Specifically, what (the second sacrifice layer) is to be removedby etching is made of the metal material, and what (the protectivelayer) is to be left even after etching is made of the first inorganicmaterial. Accordingly, when forming the space, the etching selectivityof the protective layer to the sacrifice layer (the second sacrificelayer) can be increased. Therefore, even if the protective layer isexposed to an etching medium to be used for removing the secondsacrifice layer for a long period of time, the etching medium is foretching metal materials, so that erosion of the protective layer made ofthe first inorganic material can be reduced. Therefore, the shape of theprotective layer can be excellently maintained.

On the other hand, as a sacrifice layer that closes the opening end ofthe recess, when the second sacrifice layer made of a metal material isused, if the second sacrifice layer remains on the fixed electrodeand/or the movable electrode, an operation failure of the sensor mayoccur by the second sacrifice layer. For example, if the secondsacrifice layer remains across the fixed electrode and the movableelectrode, a short-circuit occurs between the fixed electrode and themovable electrode via this second sacrifice layer.

Therefore, as a sacrifice layer that closes the opening end of therecess, the first sacrifice layer made of the second inorganic materialis used. Accordingly, while etching selectivity of the protective layerto the first sacrifice layer is secured, the operation failure of thesensor can be prevented from occurring due to the sacrifice layerremaining.

The description that the protective layer has etching selectivity to thesacrifice layer means that, for example, the materials of these layerssatisfy a ratio (etching selectivity) of the etching rate of thesacrifice layer with a certain etching medium to the etching rate of theprotective layer with this etching medium=(etching rate of protectivelayer/etching rate of sacrifice layer)≠1.

The first sacrifice layer and the second sacrifice layer may be made ofan inorganic material that can be etched with a fluorine-based gas and ametal material that can be etched with a chlorine-based gas,respectively.

In detail, when the protective layer is made of SiO₂, it is preferablethat the first sacrifice layer is made of SiN, and the second sacrificelayer is made of Al.

The method for manufacturing a MEMS sensor according to an aspect of thepresent invention preferably further includes a step of forming aprotective film having etching selectivity to the sacrifice layer so asto cover side walls of the fixed electrode and the movable electrodeprevious to formation of the sacrifice layer.

According to this method, the side walls of the fixed electrode and themovable electrode are covered by the protective film having etchingselectivity to the sacrifice layer. Therefore, when removing thesacrifice layer by etching, even if the etching medium comes intocontact with the side walls of the fixed electrode and the movableelectrode, erosion (damage) of the fixed electrode and the movableelectrode can be reduced. As a result, the variation in size of thefixed electrode and the movable electrode can be reduced.

The step of removing the sacrifice layer may include a step of supplyingan etching medium capable of etching the sacrifice layer from a throughhole by forming the through hole in the central portion of theprotective layer.

A MEMS sensor according to an aspect of the present invention includes asemiconductor substrate having a sensor region and a peripheral regionsurrounding the sensor region and having a cavity formed directly belowa surface layer portion of the sensor region, comb-tooth-like fixedelectrode and movable electrode that are formed by processing thesurface layer portion of the sensor region and engage with each other atan interval, and a protective layer that has a peripheral edge portionbonded to the peripheral region of the semiconductor substrate and acentral portion surrounded by the peripheral edge portion and coveringthe fixed electrode and the movable electrode while being spaced fromthe sensor region and is made of a first inorganic material.

With the present arrangement, the fixed electrode and the movableelectrode are covered by the central portion of the protective layer.Accordingly, dust, etc., can be prevented from entering the inside ofthe protective layer from the outside of the protective layer (the sideopposite to the sensor region with respect to the protective layer).Therefore, the fixed electrode and the movable electrode can beexcellently protected from dust, etc. As a result, operation failures ofthe sensor can be reduced.

In the MEMS sensor according to an aspect of the present invention, itis preferable that when the peripheral region includes a pad region inwhich electrode pads electrically connected to the fixed electrode andthe movable electrode are formed, openings for exposing the electrodepads are formed in the peripheral edge portion of the protective layer.

In the central portion of the protective layer, a through hole thatmakes communication between the inside and the outside of the protectivelayer may be formed.

The MEMS sensor according to an aspect of the present invention mayfurther include first insulating layers that are selectively embedded inthe fixed electrode and insulate and separate certain portions of thefixed electrode from other portions of the fixed electrode. Further, theMEMS sensor according to an aspect of the present invention may furtherinclude second insulating layers that are selectively embedded in themovable electrode and insulate and separate certain portions of themovable electrode from other portions of the movable electrode.

The protective layer may be made of SiO₂ or SiN.

In the MEMS sensor according to an aspect of the present invention, thesemiconductor substrate is preferably a conductive silicon substrate.

When the semiconductor substrate is a conductive silicon substrate, evenwithout applying a special treatment for giving conductivity to thefixed electrode and movable electrode molded to have predeterminedshapes, the molded structures can be used as they are as electrodes.Portions except for the portions to be used as electrodes can be used aswirings.

The MEMS sensor according to an aspect of the present invention mayinclude an acceleration sensor that detects acceleration applied to theMEMS sensor by detecting a change in capacitance between the fixedelectrode and the movable electrode.

The MEMS sensor according to an aspect of the present invention mayinclude an angular velocity sensor that drives the movable electrode indirections approaching and away from the cavity and detects an angularvelocity applied to the MEMS sensor at the time of this driving bydetecting a change in capacitance between the movable electrode and thefixed electrode.

A MEMS package according to an aspect of the present invention includesthe MEMS sensor and a resin package formed to cover the MEMS sensor.

With the present arrangement, the MEMS sensor according to an aspect ofthe present invention is used. Therefore, in the MEMS sensor, dust,etc., can be prevented from entering the inside of the protective layerfrom the outside, so that operation failures of the sensor can bereduced. As a result, a MEMS package with a highly reliable MEMS sensorcan be provided.

The MEMS package according to an aspect of the present invention mayfurther include an integrated circuit that is electrically connected tothe MEMS sensor and covered together with the MEMS sensor by the sameresin package. When the MEMS package according to an aspect of thepresent invention further includes a substrate that has a surface and aback surface and supports the MEMS sensor by the surface, the resinpackage may seal the MEMS sensor so as to cover the surface of thesubstrate and expose the back surface of the substrate.

A method for manufacturing a MEMS sensor according to another aspect ofthe present invention includes the steps of selectively forming a lowerelectrode on a semiconductor substrate, laminating an electrode coatingfilm made of a material having etching selectivity to polysilicon on thesemiconductor substrate so as to coat the lower electrode, selectivelyforming a sacrifice polysilicon layer on the electrode coating film,laminating a sacrifice oxide film on the electrode coating film so as tocoat the sacrifice polysilicon layer, forming an electrode polysiliconlayer on the sacrifice oxide film, forming an upper electrode byselectively etching the electrode polysilicon layer, forming aprotective film having etching selectivity to polysilicon so as to coverside walls of the upper electrode, exposing the sacrifice polysiliconlayer by removing portions of the sacrifice oxide film, and forming acavity directly below the upper electrode by removing the exposedsacrifice polysilicon layer.

According to this method, after a lower electrode is formed on asemiconductor substrate, an upper electrode is formed on thesemiconductor substrate by using an electrode polysilicon layer.Therefore, before the upper electrode is formed, the lower electrode canbe easily formed directly below the upper electrode. Further, asacrifice polysilicon layer is formed between the lower electrode andthe electrode polysilicon layer, and after the upper electrode isformed, the sacrifice polysilicon layer is removed. Therefore, a cavitycan be easily formed between the upper electrode and the lowerelectrode. Accordingly, a MEMS sensor including a capacitor consistingof an upper electrode and a lower electrode opposed vertically to eachother via a cavity can be manufactured.

This MEMS sensor includes, for example, a semiconductor substrate, alower electrode selectively formed on the semiconductor substrate, anelectrode coating film made of an insulating material and formed on thesemiconductor substrate so as to coat the lower electrode, and apolysilicon layer having an upper electrode formed at an interval abovethe electrode coating film and opposed to the lower electrode via theelectrode coating film.

With the present arrangement, the lower electrode is formed along thesurface of the semiconductor substrate. Therefore, by adjusting the areaof the lower electrode, the capacitance of the capacitor consisting ofthe upper electrode and the lower electrode can be controlled to theoptimum capacitance for sensor operations.

In addition, even after the cavity is formed by removing the sacrificepolysilicon layer, the lower electrode is covered by the electrodecoating film. Therefore, even if the upper electrode approaches thelower electrode, the upper electrode and the lower electrode can beprevented from coming into contact with each other. As a result, theupper electrode and the lower electrode can be prevented from beingshort-circuited by each other. Therefore, operation failures of thesensor can be reduced.

As a result, with the MEMS sensor according to another aspect of thepresent invention, the detection accuracy of the sensor can be improved.

In the method for manufacturing a MEMS sensor according to anotheraspect of the present invention, the step of forming the upper electrodepreferably includes a step of molding the electrode polysilicon layerinto comb-tooth-like fixed electrode and movable electrode that engagewith each other at an interval.

By this method, the MEMS sensor according to another aspect of thepresent invention in which the upper electrode includes comb-tooth-likefixed electrode and movable electrode that engage with each other at aninterval can be manufactured.

In this MEMS sensor, the capacitor consisting of the fixed electrode andthe movable electrode can be used for sensor operations. Accordingly,the capacitor relating to the detection operations of the sensor can beincreased, so that the detection accuracy of the sensor can be furtherimproved.

The method for manufacturing a MEMS sensor according to another aspectof the present invention preferably further includes a step of removingthe protective film from the side walls of the fixed electrode and themovable electrode after removing the sacrifice polysilicon layer.

In the manufactured MEMS sensor, if the protective film remains on theside walls of the fixed electrode and the movable electrode, the fixedelectrode and the movable electrode are easily electrically charged ascompared with a case where no protective film remains. Therefore, forexample, when a voltage X (V) is applied between the fixed electrode andthe movable electrode, the sensor may erroneously recognize a potentialdifference between the fixed electrode and the movable electrode causedby electric charging as a voltage applied between the fixed electrodeand the movable electrode, that is, a so-called memory effect may occur.As a result, a voltage smaller than the voltage X (V) may be appliedbetween the fixed electrode and the movable electrode and the designeddetection performance may not be realized.

Therefore, in the MEMS sensor manufactured by this method, the sidewalls of the fixed electrode and the movable electrode are exposed.Therefore, occurrence of the above-described memory effect can bereduced. As a result, a necessary and sufficient voltage can be appliedbetween the fixed electrode and the movable electrode, and the designeddetection performance can be reliably realized.

Preferably, the method for manufacturing a MEMS sensor according toanother aspect of the present invention further includes a step offorming an opening that penetrates through the electrode coating filmand selectively exposes the lower electrode previous to formation of theelectrode polysilicon layer, and the step of forming the electrodepolysilicon layer includes a step of forming the electrode polysiliconlayer on the sacrifice oxide film and concurrently, making a portion ofthe electrode polysilicon layer enter the opening of the electrodecoating film and come into contact with the lower electrode, and thestep of forming the upper electrode includes a step of forming a contactelectrode that is separated from the upper electrode and in contact withthe lower electrode.

By this method, the MEMS sensor according to another aspect of thepresent invention in which the polysilicon layer further includes acontact electrode that penetrates through the electrode coating film andis in contact with the lower electrode can be manufactured.

In this MEMS sensor, by using a portion of the electrode polysiliconlayer forming the upper electrode, a contact electrode is formed in thesame layer as that of the upper electrode. Therefore, the contacts withthe upper electrode and the lower electrode can be collectively formedin the same layer (polysilicon layer).

As a result, for example, when a wiring is formed on the contactelectrode, the contact wiring for the upper electrode can be formed inthe same step. As a result, the number of manufacturing steps can bereduced and the cost can be reduced.

By this manufacturing method, the MEMS sensor according to anotheraspect of the present invention further including a wiring on thecontact electrode can be manufactured.

The step of forming a wiring on the contact electrode may include a stepof forming a wiring on the upper electrode as well, concurrently.

The MEMS sensor according to another aspect of the present invention mayinclude an acceleration sensor that detects acceleration applied to theMEMS sensor by detecting a change in capacitance between the lowerelectrode and the movable electrode.

With the present arrangement, acceleration can be detected by aplurality of capacitors including a capacitor consisting of the lowerelectrode and the movable electrode and a capacitor consisting of thefixed electrode and the movable electrode. Therefore, the accelerationapplied to the sensor can be accurately detected.

The MEMS sensor according to another aspect of the present invention mayinclude an angular velocity sensor that drives the movable electrode indirections approaching and away from the lower electrode, and detects anangular velocity applied to the MEMS sensor at the time of this drivingby detecting a change in capacitance between the movable electrode andthe fixed electrode.

With the present arrangement, by adjusting the area of the lowerelectrode, the area of the lower electrode with respect to the movableelectrode can be made larger than the area of the fixed electrode withrespect to the movable electrode. Therefore, as compared with the casewhere a drive voltage is applied between the fixed electrode and themovable electrode that engage with each other like comb teeth, themovable electrode can be oscillated with a large amplitude. As a result,the angular velocity detection sensitivity can be improved.

In the MEMS sensor according to another aspect of the present invention,it is preferable that the lower electrode is formed along a directionacross the comb teeth of the movable electrode so as to be opposed tothe entire comb-tooth-like movable electrode.

With the present arrangement, the lower electrode can be opposed with alarge area to the movable electrode, so that the capacitance of thecapacitor between the lower electrode and the movable electrode can beincreased. As a result, the detection accuracy of the sensor can beimproved.

The electrode coating film may be made of SiO₂. The side walls of theupper electrode may be covered by a protective thin film made of aninsulating material.

A MEMS package according to another aspect of the present inventionincludes the MEMS sensor according to another aspect of the presentinvention and a resin package formed to cover the MEMS sensor.

With the present arrangement, the MEMS sensor according to anotheraspect of the present invention is used. Therefore, in the MEMS sensor,the capacitance of the capacitor consisting of the upper electrode andthe lower electrode can be controlled to an optimum capacitance forsensor operations, and the upper electrode and the lower electrode canbe prevented from being short-circuited by each other. As a result, aMEMS package with a MEMS sensor having excellent detection accuracy canbe provided.

The MEMS package according to another aspect of the present inventionmay further include an integrated circuit electrically connected to theMEMS sensor and covered together with the MEMS sensor by the same resinpackage. When the MEMS package according to another aspect of thepresent invention further includes a substrate that has a surface and aback surface and supports the MEMS sensor by the surface, the resinpackage may seal the MEMS sensor so as to cover the surface of thesubstrate and expose the back surface of the substrate.

A method for manufacturing a MEMS sensor according to still anotheraspect of the present invention includes the steps of forming a basefilm made of a material having etching selectivity to Si on a Sisubstrate, forming a polysilicon layer on the base film, formingtrenches from the surface of the polysilicon layer to the surface of theSi substrate by selectively etching the polysilicon layer and the basefilm and concurrently, forming comb-tooth-like first electrode andsecond electrode that have a lamination structure including the basefilm and the polysilicon layer and engage with each other via thetrenches, and forming a cavity directly below the base film by etchingportions directly below the base film of the Si substrate by isotropicetching by supplying an etching medium into the trenches.

According to this method, the lowest layers of the first electrode andthe second electrode are formed of the base film having etchingselectivity to Si. Therefore, when a cavity is formed by isotropicetching of the Si substrate, even if the etching medium comes intocontact with the first electrode and the second electrode, erosion ofthe first electrode and the second electrode can be reduced. As aresult, a MEMS sensor with the first electrode and the second electrodewith less variation in size can be manufactured.

Such a MEMS sensor includes, for example, similar to the MEMS sensoraccording to still another aspect of the present invention, a Sisubstrate having a surface layer portion on which a recess is formed,and comb-tooth-like first electrode and second electrode that aredisposed directly above the recess of the Si substrate and have alamination structure including a base film made of an insulatingmaterial and a polysilicon layer laminated in order from the side closeto the recess, and engage with each other via an interval.

With the present arrangement, the variation in size of thecomb-tooth-like first electrode and second electrode that engage witheach other is small, so that the detection accuracy of the sensor can beimproved.

The material that has etching selectivity to Si (in this paragraph,defined as material A) is, for example, a material satisfying a ratio(etching selectivity) of the etching rate of Si with a certain etchingmedium to the etching rate of the material A with this etchingmedium=(etching rate of material A/etching rate of Si)≠1. In particular,the material A is preferably a material that can make the etchingselectivity closer to 0 (zero) (etching selectivity≈0), andspecifically, the material A is preferably SiO₂.

In the method for manufacturing a MEMS sensor according to still anotheraspect of the present invention, preferably, the step of forming thebase film includes a step of processing the Si substrate into aplate-shaped base portion and columnar portions standing on the surfaceof the base portion by selectively etching the Si substrate, and a stepof altering the surface of the base portion and the columnar portionsinto insulating films by thermally oxidizing the surface of the baseportion and the columnar portions, and the step of selectively etchingthe polysilicon layer and the base film includes a step of etching toinsulate the first electrode and/or the second electrode from otherportions of the polysilicon layer by the columnar portions altered intothe insulating films, respectively.

By this method, the MEMS sensor according to still another aspect of thepresent invention further including first insulating layers that areembedded in the first electrode so as to penetrate through thepolysilicon layer and reach the base film and selectively insulatecertain portions of the first electrode from other portions of thepolysilicon layer, can be manufactured. Further, the MEMS sensoraccording to still another aspect of the present invention furtherincluding second insulating layers that are embedded in the secondelectrode so as to reach the base film by penetrating through thepolysilicon layer and selectively insulate certain portions of thesecond electrode from other portions of the polysilicon layer, can bemanufactured.

In the invention described in Patent Document 1 (United States PatentPublication No. 6792804), a plurality of portions that should beelectrically insulated of the Si substrate are isolated by isolationjoints (isolation joints 160, 360 . . . ). The isolation joints areformed by forming trenches in the Si substrate and thermally oxidizingthe inner walls (side walls and bottom walls) of the trenches as shownin FIG. 6 a of Patent Document 1. When the inner walls of the trenchesare thermally oxidized, SiO₂ grows from the side walls and the bottomwalls toward the insides of the trenches, and SiO₂ that grew from thewalls are eventually integrated together. Due to this integration, theisolation joint (612 in FIG. 6 a) embedded in the trenches is obtained.However, the isolation joint to be thus obtained is a film formed byintegrating multiple SiO₂ growing inside the trenches that wereoriginally void, so that the strength thereof is not so high, andformation takes time.

In the method for manufacturing a MEMS sensor according to still anotheraspect of the present invention, the shapes of the first insulatinglayers and the second insulating layers are formed as columnar portionsby etching the Si substrate with a neat crystal structure. Next, thecolumnar portions are altered into insulating films by thermaloxidization. Next, around the insulating films, a polysilicon layer isformed and etched into the shapes of the first electrode and the secondelectrode. Specifically, in this manufacturing method, the shapes of thefirst insulating layers and the second insulating layers are formed byetching the Si, so that they can be formed as insulating layers havinghigh strength in a short time as compared with the isolation jointforming method described in Patent Document 1.

In the method for manufacturing a MEMS sensor according to still anotheraspect of the present invention, the step of forming the polysiliconlayer preferably includes a step of depositing a polysilicon material toa position higher than the top portions of the columnar portions on thebase portion, and a step of grinding the polysilicon material until thesurfaces of the deposited polysilicon material are lowered to thepositions of the heights of the top portions of the columnar portions.

By this method, a polysilicon layer having thicknesses equal to theheights of the insulating films formed of the columnar portions can beformed. Therefore, certain portions of the first electrode and thesecond electrode can be reliably insulated from other portions of thepolysilicon layer.

The method for manufacturing a MEMS sensor according to still anotheraspect of the present invention preferably further includes a step offorming a protective film having etching selectivity to polysilicon soas to cover the side walls of the first electrode and the secondelectrode.

According to this method, the side walls of the first electrode and thesecond electrode are covered by the protective film having etchingselectivity to Si. Therefore, when a cavity is formed by isotropicetching of the Si substrate, even if an etching medium comes intocontact with the side walls of the first electrode and the secondelectrode, erosion of the first electrode and the second electrode canbe reduced. As a result, the variation in size of the first electrodeand the second electrode can be further reduced.

The method for manufacturing a MEMS sensor according to still anotheraspect of the present invention preferably includes a step ofselectively forming wirings on the polysilicon layer previous toformation of the trenches.

According to this method, wirings are formed on the polysilicon layerbefore the polysilicon layer is molded into complicated comb-tooth-likefirst electrode and second electrode, so that the wirings for contactwith the first electrode and the second electrode can be easily formed.

In the MEMS sensor according to still another aspect of the presentinvention, the first electrode may be a movable electrode and the secondelectrode may be a fixed electrode. Alternatively, the first electrodemay be a fixed electrode and the second electrode may be a movableelectrode.

The MEMS sensor according to still another aspect of the presentinvention may include an acceleration sensor that detects accelerationapplied to the MEMS sensor by detecting a change in capacitance betweenthe first electrode and the second electrode.

With the present arrangement, acceleration can be detected by acapacitor consisting of the first electrode and the second electrodewith less variation in size. Therefore, acceleration applied to thesensor can be accurately detected.

The MEMS sensor according to still another aspect of the presentinvention may include an angular velocity sensor that drives the firstelectrode in directions approaching and away from the recess and detectsan angular velocity applied to the MEMS sensor at the time of thisdriving by detecting a change in capacitance between the first electrodeand the second electrode.

With the present arrangement, the variation in size of the firstelectrode is small, so that the first electrode can be driven asdesigned. Therefore, an angular velocity applied to the sensor can beaccurately detected.

In the MEMS sensor according to still another aspect of the presentinvention, the thickness of the base film may be 2 μm to 10 μm. Thethickness of the polysilicon layer may be 5 μm to 20 μm.

A MEMS package according to still another aspect of the presentinvention includes the MEMS sensor according to still another aspect ofthe present invention and a resin package formed to cover the MEMSsensor.

With the present arrangement, the MEMS sensor according to still anotheraspect of the present invention is used. Therefore, in the MEMS sensor,the variation in size of the comb-tooth-like first electrode and secondelectrode that engage with each other can be reduced, so that thedetection accuracy of the sensor can be improved. As a result, a MEMSpackage including a MEMS sensor with excellent detection accuracy can beprovided.

The MEMS package according to still another aspect of the presentinvention may further include an integrated circuit electricallyconnected to the MEMS sensor and covered together with the MEMS sensorby the same resin package. When the MEMS package according to stillanother aspect of the present invention further includes a substratethat has a surface and a back surface and supports the MEMS sensor bythe surface, the resin package may seal the MEMS sensor so as to coverthe surface of the substrate and expose the back surface of thesubstrate.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

(1) First Preferred Embodiment <Entire Arrangement of Gyro Sensor>

FIG. 1 is a schematic plan view of a gyro sensor according to a firstpreferred embodiment of the present invention.

The gyro sensor 1A is a capacitance type angular velocity sensor thatdetects an angular velocity based on a change in capacitance of acapacitor, and is used for, for example, correcting shake of a videocamera or a still camera, detecting a position of a car navigationsystem, and detecting motions of a robot and a gaming machine, etc.

The gyro sensor 1A includes a semiconductor substrate 2A quadrilateralin a plan view, a sensor portion 3A disposed at the central portion ofthe semiconductor substrate 2A, and electrode pads 4A that are disposedon the lateral side of the sensor portion 3A on the semiconductorsubstrate 2A and for supplying voltages to the sensor portion 3A.

The sensor portion 3A includes an X-axis sensor 5A, a Y-axis sensor 6A,and Z-axis sensors 7A as sensors that respectively detect angularvelocities around the three axes orthogonal to each other in thethree-dimensional space. These three sensors 5A to 7A are covered andsealed by a lid substrate 8A by, for example, bonding the lid substrate8A formed of a silicon substrate to the surface of a semiconductorsubstrate 2A.

The X-axis sensor 5A generates a coriolis force Fz in the Z-axisdirection by using oscillation Ux in the X-axis direction when the gyrosensor 1A is tilted, and detects an angular velocity ωy applied aroundthe Y axis by detecting a change in capacitance caused by the coriolisforce. The Y-axis sensor 6A generates a coriolis force Fx in the X-axisdirection by using oscillation Uy in the Y-axis direction when the gyrosensor 1A is tilted, and detects an angular velocity ωz applied aroundthe Z axis by detecting a change in capacitance caused by the coriolisforce. The Z-axis sensor 7A generates a coriolis force Fy in the Y-axisdirection by using oscillation Uz in the Z-axis direction when the gyrosensor 1A is tilted, and detects an angular velocity ωx applied aroundthe X-axis by detecting a change in capacitance caused by the coriolisforce.

A plurality (five in FIG. 1) of electrode pads 4A are provided at evenintervals.

<Arrangement of X-Axis Sensor and Y-Axis Sensor>

Next, the arrangement of the X-axis sensor and the Y-axis sensor will bedescribed with reference to FIG. 2 to FIG. 4.

FIG. 2 is a schematic plan view of a sensor portion shown in FIG. 1.FIG. 3 is a plan view of a principal portion of the X-axis sensor shownin FIG. 2. FIG. 4 is a sectional view of the principal portion of theX-axis sensor shown in FIG. 2, illustrating a section taken along thecutting plane A-A in FIG. 3.

The semiconductor substrate 2A is formed of a conductive siliconsubstrate (low-resistance substrate with a resistivity of, for example,5 Ω·m to 500 Ω·m). This semiconductor substrate 2A has a cavity 10Ainside, and in the upper wall 11A (surface portion) of the semiconductorsubstrate 2A having a ceiling that partitions the cavity 10A from thesurface side, the X-axis sensor 5A, the Y-axis sensor 6A, and the Z-axissensors 7A are formed. Specifically, the X-axis sensor 5A, the Y-axissensor 6A, and the Z-axis sensors 7A are formed of portions of thesemiconductor substrate 2A, and are supported while in a floating statewith respect to the bottom wall 12A of the semiconductor substrate 2Athat has a bottom surface partitioning the cavity 10A from the backsurface side.

The X-axis sensor 5A and the Y-axis sensor 6A are disposed adjacent toeach other at an interval, and the Z-axis sensors 7A are disposed tosurround the X-axis sensor 5A and Y-axis sensor 6A, respectively. In thepresent preferred embodiment, the Y-axis sensor 6A has an arrangementthat is substantially the same as an arrangement obtained by rotating 90degrees the X-axis sensor 5A in a plan view. Therefore, hereinafter,instead of a detailed description of the arrangement of the Y-axissensor 6A, in the description of the portions of the X-axis sensor 5A,portions of the Y-axis sensor corresponding to the portions of theX-axis sensor are also described with parentheses.

Between the X-axis sensor 5A and the Z-axis sensor 7A and between theY-axis sensor 6A and the Z-axis sensor 7A, support portions 14A forsupporting these in a floating state are formed. The support portions14A integrally include straight portions 16A extending across the Z-axissensors 7A from one side walls 15A having side surfaces that partitionthe cavity 10A of the semiconductor substrate 2A from the lateral sidestoward the X-axis sensor 5A and the Y-axis sensor 6A, and annularportions 17A surrounding the X-axis sensor 5A and the Y-axis sensor 6A.

The X-axis sensor 5A and the Y-axis sensor 6A are disposed inside theannular portions 17A, and both ends of these sensors are supported attwo points opposing each other on the inner walls of the annularportions 17A. Both ends of the Z-axis sensors 7A are supported on bothside walls of the straight portions 16A.

The X-axis sensor 5A (Y-axis sensor 6A) includes an X fixed electrode21A (Y fixed electrode 41A) fixed to the support portion 14A providedinside the cavity 10A, and an X movable electrode 22A (Y movableelectrode 42A) held to be capable of oscillating with respect to the Xfixed electrode 21A. The X fixed electrode 21A and the X movableelectrode 22A are formed to have the same thickness.

The X fixed electrode 21A (Y fixed electrode 41A) includes a baseportion 23A (base portion 43A of the Y fixed electrode 41A) that isfixed to the support portion 14A and has a quadrilateral annular shapein a plan view, and a plurality of pairs of comb tooth portions 24A(comb tooth portions 44A of the Y fixed electrode 41A) aligned like combteeth at even intervals along the inner wall of the base portion 23A.

On the other hand, the X movable electrode 22A (Y movable electrode 42A)includes a base portion 26A (base portion 46A of the Y movable electrode42A) that extends in a direction across the comb tooth portions 24A ofthe X fixed electrode 21A and has both ends connected to the baseportion 23A of the X fixed electrode 21A via expandable beam portions25A (beam portions 45A of the Y-axis sensor 6A) along the directionacross the comb tooth portions 24A, and comb tooth portions 27A (combtooth portions 47A of the Y movable electrode 42A) that extend from thebase portion 26A to both sides toward the portions between the combtooth portions 24A adjacent to each other of the X fixed electrode 21A,and are aligned like comb teeth that engage with the comb tooth portions24A of the X fixed electrode 21A without contact.

In the X-axis sensor 5A, when the beam portions 25A expand and contractand the base portion 26A of the X movable electrode 22A oscillates alongthe surface of the semiconductor substrate 2A (oscillation Ux), the combtooth portions 27A of the X movable electrode 22A that engage with thecomb tooth portions 24A like comb teeth of the X fixed electrode 21Aoscillate alternately in directions approaching and away from the combtooth portions 24A of the X fixed electrode 21A.

The base portion 23A of the X fixed electrode 21A has a truss-shapedframed structure including straight main frames extending parallel toeach other and reinforcing frames combined with the main frames so thata triangular space is repeatedly formed along the main frames.

As the comb tooth portions 24A of the X fixed electrode 21A, twoelectrode portions straight in a plan view that have base end portionsconnected to the base portion 23A and tip end portions thereof opposedto each other are paired, and a plurality of the pairs are provided ateven intervals. Each comb tooth portion 24A has a framed structurehaving a ladder-like shape in a plan view including straight main framesextending parallel to each other and a plurality of traverse frames laidacross the main frames.

On the other hand, the base portion 26A of the X movable electrode 22Ais formed of a plurality (six in the present preferred embodiment) ofstraight frames extending parallel to each other, and both ends thereofare connected to beam portions 25A. Two beam portions 25A are providedon each of both ends of the base portion 26A of the X movable electrode22A.

Each comb tooth portion 27A of the X movable electrode 22A has a framedstructure having a ladder-like shape in a plan view including straightmain frames extending parallel to each other across the frames of thebase portion 26A and a plurality of traverse frames laid across the mainframes.

In the X movable electrode 22A, on lines halving the comb tooth portions27A in a direction orthogonal to the oscillation direction Ux,insulating layers 28A (silicon oxide in the present preferredembodiment) across the traverse frames are embedded from the surface tothe cavity 10A. By the insulating layer 28A, each comb tooth portion 27Ais insulated and separated into two of one side and the other side alongthe oscillation direction Ux. Accordingly, the separated comb toothportions 27A of the X movable electrode 22A function as independentelectrodes respectively in the X movable electrode 22A.

On the surface of the semiconductor substrate 2A including the X fixedelectrode 21A and the X movable electrode 22A, a first insulating film33A and a second insulating film 34A made of silicon oxide (SiO₂) arelaminated in order, and on this second insulating film 34A, an X firstdrive/detection wiring 29A (Y first drive/detection wiring 49A) and an Xsecond drive/detection wiring 30A (Y second drive/detection wiring 50A)are formed.

The X first drive/detection wiring 29A supplies a drive voltage to oneside (the left side on the paper surface shown in FIG. 3 in the presentpreferred embodiment) of each comb tooth portion 27A insulated andseparated into two, and detects a change in voltage accompanying achange in capacitance from the comb tooth portion 27A. On the otherhand, the X second drive/detection wiring 30A supplies a drive voltageto the other side (the right side on the paper surface shown in FIG. 3in the present preferred embodiment) of each comb tooth portion 27Ainsulated and separated into two, and detects a change in voltageaccompanying a change in capacitance from the comb tooth portion 27A.

The X first and X second drive/detection wirings 29A and 30A are made ofaluminum (Al) in the present preferred embodiment. The X first and Xsecond drive/detection wirings 29A and 30A are electrically connected tothe comb tooth portions 27A by penetrating through the first and secondinsulating films 33A and 34A.

The X first and X second drive/detection wirings 29A and 30A are ledonto the support portion 14A via the beam portions 25A of the X movableelectrode 22A and the base portion 23A of the X fixed electrode 21A, andare partially exposed as electrode pads 4A. The X first and X seconddrive/detection wirings 29A and 30A use the beam portions 25A themselvesformed of portions of the conductive semiconductor substrate 2A ascurrent paths in sections passing through the beam portions 25A of the Xmovable electrode 22A, respectively. No aluminum wiring is provided onthe beam portions 25A, so that the expandability of the beam portions25A can be maintained.

To the support portion 14A, an X third drive/detection wiring 32A thatdetects a change in voltage caused by a change in capacitance from thecomb tooth portions 24A of the X fixed electrode 21A is led, and this Xthird drive/detection wiring 32A is also partially exposed as anelectrode pad 4A (not shown) in the same manner as other wirings 29A and30A.

On the semiconductor substrate 2A, the upper surfaces and the sidesurfaces of the X fixed electrode 21A and the X movable electrode 22Aare coated together with the first insulating film 33A and the secondinsulating film 34A by a protective thin film 35A made of silicon oxide(SiO₂).

On portions except for the cavity 10A of the surface of thesemiconductor substrate 2A, a third insulating film 36A, a fourthinsulating film 37A, a fifth insulating film 38A, and a surfaceprotective film 39A are laminated in order on the second insulating film34A.

In the X-axis sensor 5A structured as described above, drive voltageswith the same polarity and drive voltages with different polarities arealternately applied between the X fixed electrode 21A and the X movableelectrode 22A via the X first to X third drive/detection wirings 29A,30A, and 32A. Accordingly, between the comb tooth portions 24A of the Xfixed electrode 21A and the comb tooth portions 27A of the X movableelectrode 22A, coulomb repulsive and attractive forces are alternatelygenerated. As a result, the comb-tooth-like X movable electrode 22Aoscillates similarly to the left and right along the X-axis directionwith respect to the comb-tooth-like X fixed electrode 21A (oscillationUx). In this state, when the X movable electrode 22A rotates around theY axis as a central axis, a coriolis force Fz is generated in the Z-axisdirection. This coriolis force Fz changes the opposing area and/ordistance between the comb tooth portions 24A of the X fixed electrode21A and the comb tooth portions 27A of the X movable electrode 22Aadjacent to each other. Then, by detecting a change in capacitancebetween the X movable electrode 22A and the X fixed electrode 21A causedby the change in opposing area and/or distance, the angular velocity ωyaround the Y axis is detected.

In the present preferred embodiment, the angular velocity ωy around theY axis is obtained by calculating a difference between detection valuesof one-side and the other-side electrode portions insulated andseparated from each other of the X movable electrode 22A.

In the Y-axis sensor 6A, drive voltages with the same polarity and drivevoltages with different polarities are alternately applied between the Yfixed electrode 41A and the Y movable electrode 42A via the Y first to Ythird drive/detection wirings 49A, 50A, and 52A. Accordingly, coulombrepulsive and attractive forces are alternately generated between thecomb tooth portions 44A of the Y fixed electrode 41A and the comb toothportions 47A of the Y movable electrode 42A. As a result, thecomb-tooth-like Y movable electrode 42A oscillates similarly to the leftand right along the Y-axis direction with respect to the comb-tooth-likeY fixed electrode 41A (oscillation Uy). In this state, when the Ymovable electrode 42A rotates around the Y axis as a central axis, acoriolis force Fx is generated in the X-axis direction. This coriolisforce Fx changes the opposing area and/or distance between the combtooth portions 44A of the Y fixed electrode 41A and the comb toothportions 47A of the Y movable electrode 42A adjacent to each other.Then, by detecting a change in capacitance between the Y movableelectrode 42A and the Y fixed electrode 41A caused by the change inopposing area and/or distance, the angular velocity ωz around the Z axisis detected.

<Arrangement of Z-Axis Sensors>

Next, an arrangement of the Z-axis sensors will be described withreference to FIG. 2, FIG. 5, and FIG. 6.

FIG. 5 is a plan view of a principal portion of the Z-axis sensor shownin FIG. 2. FIG. 6 is a sectional view of the principal portion of theZ-axis sensor shown in FIG. 2, illustrating a section taken along thecutting plane B-B in FIG. 5.

Referring to FIG. 2, the semiconductor substrate 2A made of conductivesilicon has a cavity 10A inside as described above. In the upper wall11A (surface portion) of the semiconductor substrate 2A, the Z-axissensors 7A supported by the support portions 14A while in a floatingstate with respect to the bottom wall 12A of the semiconductor substrate2A are disposed to surround the X-axis sensor 5A and the Y-axis sensor6A, respectively.

Each Z-axis sensor 7A includes a Z fixed electrode 61A as a firstelectrode fixed to the support portion 14A (straight portion 16A)provided inside the cavity 10A, and a Z movable electrode 62A as asecond electrode held to be capable of oscillating with respect to the Zfixed electrode 61A. The Z fixed electrode 61A and the Z movableelectrode 62A are formed to have the same thickness.

In one Z-axis sensor 7A of these two Z-axis sensors 7A, the Z movableelectrode 62A is disposed to surround the annular portion 17A of thesupport portion 14A, and the Z fixed electrode 61A is disposed tofurther surround the Z movable electrode 62A. In the other Z-axis sensor7A, the Z fixed electrode 61A is disposed to surround the annularportion 17A of the support portion 14A, and the Z movable electrode 62Ais disposed to further surround the Z fixed electrode 61A. The Z fixedelectrode 61A and the Z movable electrode 62A are connected integrallyto both side walls of the straight portion 16A of the support portion14A.

The Z fixed electrode 61A includes a first base portion 63A having aquadrilateral annular shape in a plan view fixed to the support portion14A, and a plurality of comb-tooth-like first comb tooth portions 64Aprovided on the portion opposite to the straight portion 16A withrespect to the X-axis sensor 5A (Y-axis sensor 6A) of the first baseportion 63A.

On the other hand, the Z movable electrode 62A includes a second baseportion 65A having a quadrilateral annular shape in a plan view, andcomb-tooth-like second comb tooth portions 66A extending from the secondbase portion 65A toward the portions between the comb-tooth-like firstcomb tooth portions 64A of the Z fixed electrode 61A adjacent to eachother that engage with the first comb tooth portions 64A of the Z fixedelectrode 61A without contact. The second base portion 65A of the Zmovable electrode 62A has a truss-shaped framed structure includingstraight main frames extending parallel to each other and reinforcingframes combined with the main frames so that a triangular space isrepeatedly formed along the main frames. The second base portion 65A ofthe Z movable electrode 62A thus structured has sections in which thereinforcing frames are omitted at portions on the side opposite to theside of disposition of the second comb tooth portions 66A, and the mainframes in the sections function as beam portions 67A for enabling the Zmovable electrode 62A to move up and down.

Specifically, in this Z-axis sensor 7A, the beam portions 67Aelastically warp, and the second base portion 65A of the Z movableelectrode 62A turns like a pendulum in directions approaching and awayfrom the cavity 10A around the beam portions 67A as pivot points(oscillation Uz), and accordingly, the second comb tooth portions 66A ofthe Z movable electrode 62A engaging with the first comb tooth portions64A of the Z fixed electrode 61A like comb teeth oscillate up and down.

The first base portion 63A of the Z fixed electrode 61A has atruss-shaped framed structure including straight main frames extendingparallel to each other and reinforcing frames combined with the mainframes so that a triangular space is repeatedly formed along the mainframes.

The first comb tooth portions 64A of the Z fixed electrode 61A have baseend portions connected to the first base portion 63A of the Z fixedelectrode 61A and tip end portions extending toward the Z movableelectrode 62A, and are aligned like comb teeth at even intervals alongthe inner wall of the first base portion 63A. In portions close to thebase end portions of the first comb tooth portions 64A, insulatinglayers 68A (silicon oxide in the present preferred embodiment) areembedded across the first comb tooth portions 64A in the width directionfrom the surface to the cavity 10A. By the insulating layers 68A, thefirst comb tooth portions 64A of the Z fixed electrode 61A are insulatedfrom other portions of the Z fixed electrode 61A.

In the first base portion 63A of the Z fixed electrode 61A, on bothsides of a portion (opposed portion 84A) opposed to the tip end portion70A (described later) of each second comb tooth portion 66A of the Zmovable electrode 62A, insulating layers 69A as first separating andinsulating layers are embedded across the main frame of the trussstructure in the width direction from the surface to the cavity 10A ofthe semiconductor substrate 2A. Accordingly, the opposed portion 84Asurrounded by the insulating layers 69A and the triangular space of thetruss structure is insulated from other portions of the first baseportion 63A of the Z fixed electrode 61A.

To the opposed portions 84A, the first drive portions 18A extendingtoward the tip end portions 70A (described later) of the second combtooth portions 66A disposed in front of the opposed portions areconnected integrally. Specifically, the first drive portions 18A areprovided between the first comb tooth portions 64A aligned like combteeth on the first base portion 63A of the Z fixed electrode 61A.Therefore, on the entire first base portion 63A of the Z fixed electrode61A, the first comb tooth portions 64A and the first drive portions 18Ashorter than the first comb tooth portions 64A are aligned like combteeth at even intervals.

On the other hand, the second comb tooth portions 66A of the Z movableelectrode 62A have base end portions 71A connected to the second baseportion 65A of the Z movable electrode 62A and tip end portions 70Aextending toward the portions between the first comb tooth portions 64Aof the Z fixed electrode 61A, and are aligned like comb teeth thatengage with the first comb tooth portions 64A of the Z fixed electrode61A without contact therebetween. In portions close to the tip endportions 70A of the second comb tooth portions 66A of the Z movableelectrode 62A, insulating layers 73A (silicon oxide in the presentpreferred embodiment) as second separating and insulating layers areembedded across the second comb tooth portions 66A in the widthdirection from the surface to the cavity 10A of the semiconductorsubstrate 2A. In portions close to the base end portions 71A of thesecond comb tooth portions 66A of the Z movable electrode 62A,insulating layers 74A (silicon oxide in the present preferredembodiment) are embedded across the second comb tooth portions 66A inthe width direction from the surface to the cavity 10A of thesemiconductor substrate 2A. Each second comb tooth portion 66A has threeportions (the tip end portion 70A, the base end portion 71A, and theintermediate portion 72A between the tip end portion 70A and the baseend portion 71A) insulated from other portions by these insulatinglayers 73A and 74A.

The tip end portions 70A of the second comb tooth portions 66Aintegrally include second drive portions 19A formed like comb teeth.Specifically, the Z movable electrode 62A includes a plurality of secondcomb tooth portions 66A aligned like comb teeth, and on the tip endportion 70A of each second comb tooth portion 66A, a second driveportion 19A having a comb-tooth-like shape smaller than the second combtooth portion 66A is formed. The second drive portions 19A engage withthe first drive portions 18A of the Z fixed electrode 61A while beingspaced from each other so as not to come into contact with each other.

On the surface of the semiconductor substrate 2A including the Z fixedelectrode 61A and the Z movable electrode 62A, a first insulating film33A and a second insulating film 34A made of silicon oxide (SiO₂) arelaminated in order as described above. On the second insulating layer34A, a Z first detection wiring 75A, Z first drive wiring 76A as a firstdetection wiring, a Z second detection wiring 77A, Z second drive wiring78A as a second detection wiring are formed. In the present preferredembodiment, the Z first detection wiring 75A and the Z first drivewiring 76A constitute a first contact wiring that comes into directcontact with the Z fixed electrode 61A from the surface side of thesemiconductor substrate 2A. Also, the Z second detection wiring 77A andthe Z second drive wiring 78A constitute a second contact wiring thatcomes into direct contact with the Z movable electrode 62A from thesurface side of the semiconductor substrate 2A.

The Z first detection wiring 75A and the Z second detection wiring 77Aare connected to the first comb tooth portions 64A of the Z fixedelectrode 61A and the intermediate portions 72A of the Z movableelectrode 62A adjacent to each other, respectively. Specifically, inthis Z-axis sensor 7A, the first comb tooth portions 64A of the Z fixedelectrode 61A and the intermediate portions 72A of the Z movableelectrode 62A to which the Z first detection wiring 75A and the Z seconddetection wiring 77A are connected are opposed to each other at anelectrode-to-electrode distance d, and constitutes electrodes of acapacitor (detector) when a fixed voltage is applied between theelectrodes and the capacitance of the capacitor changes according to achange in electrode-to-electrode distance d and/or opposing area.

In detail, the Z first detection wiring 75A is formed along the firstbase portion 63A of the Z fixed electrode 61A and includes aluminumwirings branched toward the tip end portions of the first comb toothportions 64A across the insulating layers 68A of the first comb toothportions 64A of the Z fixed electrode 61A. The branched aluminum wiringsare electrically connected to the tip end sides relative to theinsulating layers 68A of the first comb tooth portions 64A bypenetrating through the first insulating film 33A and the secondinsulating film 34A. As shown in FIG. 2, the Z first detection wiring75A is led onto the support portion 14A via the first base portion 63Aof the Z fixed electrode 61A, and is partially exposed as an electrodepad 4A.

On the other hand, the Z second detection wiring 77A detects a change involtage accompanying a change in capacitance from the second comb toothportions 66A of the Z movable electrode 62A. This Z second detectionwiring 77A is formed along the second base portion 65A of the Z movableelectrode 62A, and includes aluminum wirings branched toward theintermediate portions 72A across the insulating layers 74A close to thebase end portions 71A of the second comb tooth portions 66A of the Zmovable electrode 62A. The branched aluminum wirings are electricallyconnected to the intermediate portions 72A of the second comb toothportions 66A by penetrating through the first insulating film 33A andthe second insulating film 34A. As shown in FIG. 2, the Z seconddetection wiring 77A is led onto the support portion 14A via the secondbase portion 65A of the Z movable electrode 62A, and partially exposedas an electrode pad 4A.

The Z first drive wiring 76A and the Z second drive wiring 78A arerespectively connected to the opposed portions 84A (first drive portions18A) of the Z fixed electrode 61A and the tip end portions 70A (seconddrive portions 19A) of the Z movable electrode 62A that face each otherin a direction orthogonal to the opposing direction of electrodesconstituting a capacitor. Specifically, in this Z-axis sensor 7A, thefirst drive portions 18A of the Z fixed electrode 61A and the seconddrive portions 19A of the Z movable electrode 62A that engage with eachother like comb teeth at an interval constitute drive portions betweenwhich drive voltages are applied to oscillate the Z movable electrode62A by coulomb forces generated by changes in the drive voltages.

In detail, the Z first drive wiring 76A supplies a drive voltage to theopposed portions 84A (first drive portions 18A) of the Z fixed electrode61A. The Z first drive wiring 76A includes aluminum wirings that arelaid across both sides of the insulating layers 69A by using the surfaceof the second insulating film 34A and electrically connected to theopposed portions 84A and portions except for the opposed portions 84A ofthe first base portion 63A by penetrating through the first insulatingfilm 33A and the second insulating film 34A, and a remaining portion ofthe Z first drive wiring is formed by using the first base portion 63Aof the Z fixed electrode 61A made of conductive silicon. As shown inFIG. 2, the Z first drive wiring 76A is led onto the support portion14A, and partially exposed as an electrode pad 4A.

On the other hand, the Z second drive wiring 78A supplies a drivevoltage to the tip end portions 70A (second drive portions 19A) of the Zmovable electrode 62A. The Z second drive wiring 78A includes aluminumwirings that are laid across the tip end portions 70A and the base endportions 71A of the second comb tooth portions 66A by using the surfaceof the second insulating film 34A, and electrically connected to the tipend portions 70A and the base end portions 71A by penetrating throughthe first insulating film 33A and the second insulating film 34A, and aremaining portion of the Z second drive wiring is formed by using thesecond base portion 65A of the Z movable electrode 62A made ofconductive silicon. As shown in FIG. 2, the Z second drive wiring 78A isled onto the support portion 14A and partially exposed as an electrodepad 4A.

On the semiconductor substrate 2A, the upper surfaces and the sidesurface of the Z fixed electrode 61A and the Z movable electrode 62A arecoated together with the first insulating film 33A and the secondinsulating film 34A by the protective thin film 35A made of siliconoxide (SiO₂).

On portions except for the cavity 10A of the surface of thesemiconductor substrate 2A, the third insulating film 36A, the fourthinsulating film 37A, the fifth insulating film 38A, and the surfaceprotective film 39A are laminated in order on the second insulating film34A.

In this Z-axis sensor 7A, drive voltages with the same polarity anddrive voltages with different polarities are alternately applied betweenthe opposed portions 84A (first drive portions 18A) of the Z fixedelectrode 61A and the tip end portions 70A (second drive portions 19A)of the Z movable electrode 62A via the Z first drive wiring 76A and theZ second drive wiring 78A. Accordingly, coulomb repulsive and attractiveforces are alternately generated between the first drive portions 18A ofthe Z fixed electrode 61A and the second drive portions 19A of the Zmovable electrode 62A. As a result, the comb-tooth-like Z movableelectrode 62A oscillates up and down like a pendulum similarly aroundthe comb-tooth-like Z fixed electrode 61A as a center of oscillationalong the Z-axis direction with respect to the Z fixed electrode 61A(oscillation Uz). In this state, when the Z movable electrode 62Arotates around the X axis as a central axis, a coriolis force Fy isgenerated in the Y-axis direction. This coriolis force Fy changes theopposing area S and/or electrode-to-electrode distance d between thefirst comb tooth portions 64A of the Z fixed electrode 61A and theintermediate portions 72A of the second comb tooth portions 66A of the Zmovable electrode 62A adjacent to each other. Then, by detecting achange in capacitance C between the Z movable electrode 62A and the Zfixed electrode 61A caused by the change in opposing area S and/orelectrode-to-electrode distance d via the Z first detection wiring 75Aand the Z second detection wiring 77A, the angular velocity ωx aroundthe X axis is detected. In the present preferred embodiment, the angularvelocity ωx around the X axis is obtained by calculating a differencebetween a detection value of the Z-axis sensor 7A surrounding the X-axissensor 5A and a detection value of the Z-axis sensor 7A surrounding theY-axis sensor 6A. The difference can be provided, for example, as shownin FIG. 2, by making the position relationship of the fixed electrodeand the movable electrode of the Z-axis sensor 7A surrounding the X-axissensor 5A opposite to the position relationship of the fixed electrodeand the movable electrode of the Z-axis sensor 7A surrounding the Y-axissensor 6A. Accordingly, the manner of oscillation of the Z movableelectrode 62A differs between the pair of Z-axis sensors 7A, so that adifference occurs.

In this gyro sensor 1A, the first drive portions 18A and the seconddrive portions 19A for driving (oscillating) the Z movable electrode 62Aare disposed to engage with each other like comb teeth. Therefore, forexample, as compared with cases such as where the side walls of theopposed portions 84A of the Z fixed electrode 61A and the side walls ofthe Z movable electrode 62A are both flat and just opposed to eachother, the opposing area between the drive electrodes (in the presentpreferred embodiment, the opposing area between the side surface of thedrive portion 18A and the side surface of the second drive portion 19A)can be made larger. Therefore, the Z movable electrode 62A can beoscillated with a large amplitude, so that the detection sensitivity canbe improved.

In the gyro sensor 1A, the Z fixed electrode 61A and the Z movableelectrode 62A are formed by using the upper wall 11A of thesemiconductor substrate 2A having the cavity 10A in the surface portionof the semiconductor substrate 2A. Therefore, the thickness of theentire sensor is substantially the thickness of the semiconductorsubstrate 2A, so that the sensor can be downsized.

The insulating layers 68A, 69A, 73A and 74A for insulating andseparating the opposed portions 84A of the Z fixed electrode 61A and thebase end portions 71A, the intermediate portions 72A, and the tip endportions 70A of the Z movable electrode 62A are embedded in thesemiconductor substrate 2A, so that the surface of the semiconductorsubstrate 2A can be efficiently used as a space for leading the aluminumwirings of the X first drive/detection wiring 29A and the Z firstdetection wiring 75A, etc.

Further, the semiconductor substrate 2A is a conductive siliconsubstrate, so that even without applying a special treatment for givingconductivity to the X fixed electrode 21A, the Y fixed electrode 41A,and the Z fixed electrode 61A, and the X movable electrode 22A, the Ymovable electrode 42A, and the Z movable electrode 62A molded intopredetermined shapes, the molded structures can be used as they are aselectrodes. The portions except for the portions to be used aselectrodes can be used as wirings (the X first drive/detection wiring29A and the Z first detection wiring 75A, etc.).

<Method for Manufacturing Gyro Sensor 1A>

Next, a manufacturing process of the above-described gyro sensor will bedescribed in order of steps with reference to FIG. 7A to FIG. 7G. Inthis paragraph, only the manufacturing process of the Z-axis sensors isshown in the drawings, and the manufacturing processes of the X-axissensor and the Y-axis sensor are omitted, however, the manufacturingprocesses of the X-axis sensor and the Y-axis sensor are performed inparallel to the manufacturing process of the Z-axis sensors in the samemanner as the manufacturing process of the Z-axis sensors.

FIG. 7A to FIG. 7G are schematic sectional views showing parts of themanufacturing process of the gyro sensor according to the firstpreferred embodiment of the present invention in order of steps,illustrating a section taken along the cutting plane at the sameposition as in FIG. 6.

To manufacture this gyro sensor 1A, first, as shown in FIG. 7A, thesurface of the semiconductor substrate 2A made of conductive silicon isthermally oxidized (for example, temperature: 1100 to 1200° C., filmthickness: 5000 Å). Accordingly, the first insulating film 33A is formedon the surface of the semiconductor substrate 2A. Next, by a knownpatterning technique, the first insulating film 33A is patterned, andopenings are formed in regions in which the insulating layers 68A, 69A,73A, and 74A should be embedded. Next, by anisotropic deep RIE (ReactiveIon Etching) using the first insulating film 33A as a hard mask,specifically, by a Bosch process, the semiconductor substrate 2A is dug.Accordingly, trenches are formed in the semiconductor substrate 2A. Inthe Bosch process, a step of etching the semiconductor substrate 2A byusing SF₆ (sulfur hexafluoride) and a step of forming a protective filmon the etched surfaces by using C₄F₈ (perfluorocyclobutane) arealternately repeated. Accordingly, the semiconductor substrate 2A can beetched at a high aspect ratio, however, a wavy irregularity calledscallop is formed on the etched surfaces (inner peripheral surfaces ofthe trenches). Subsequently, the insides of the trenches formed in thesemiconductor substrate 2A and the surface of the semiconductorsubstrate 2A are thermally oxidized (for example, temperature: 1100 to1200° C.), and then, the surface of the oxide film is etched back (forexample, the film thickness after etching back is 21800 Å). Accordingly,the insulating layers 68A, 69A, 73A, and 74A filling the trenches areformed (only the insulating layer 74A is shown).

Next, as shown in FIG. 7B, by a CVD method, the second insulating film34A made of silicon oxide is laminated on the semiconductor substrate2A. Next, the second insulating film 34A and the first insulating film33A are successively etched. Accordingly, contact holes are formed inthe second insulating film 34A and the first insulating film 33A. Next,contact plugs filling the contact holes are formed, and by sputtering,aluminum is deposited (for example, 7000 Å) on the second insulatingfilm 34A, and the aluminum deposit layer is patterned. Accordingly, thewirings 75A to 78A are formed on the second insulating film 34A.

Next, as shown in FIG. 7C, by a CVD method, the third insulating film36A, the fourth insulating film 37A, the fifth insulating film 38A, andthe surface protective film 39A are laminated in order on the secondinsulating film 34A. Next, the third to fifth insulating films 36A to38A and the surface protective film 39A on the region in which thecavity 10A of the semiconductor substrate 2A should be formed areremoved by etching.

Next, as shown in FIG. 7D, a resist having openings in regions otherthan the regions in which the Z fixed electrode 61A and the Z movableelectrode 62A should be formed is formed on the second insulating film34A. Subsequently, by anisotropic deep RIE using this resist as a mask,specifically, by a Bosch process, the semiconductor substrate 2A is dug.Accordingly, the surface portion of the semiconductor substrate 2A ismolded into the shapes of the Z fixed electrode 61A and the Z movableelectrode 62A, and between these, trenches 60A are formed. In the Boschprocess, a step of etching the semiconductor substrate 2A by using SF₆(sulfur hexafluoride) and a step of forming a protective film on theetched surfaces by using C₄F₈ (perfluorocyclobutane) are alternatelyrepeated. After the deep RIE, the resist is stripped.

Next, as shown in FIG. 7E, by thermal oxidization or by a PECVD method,on the entire surfaces of the Z fixed electrode 61A and the Z movableelectrode 62A and the entire inner surfaces of the trenches 60A (thatis, the side surfaces and the bottom surfaces that define the trenches60A), the protective thin film 35A made of silicon oxide (SiO₂) isformed.

Next, as shown in FIG. 7F, by etching back, the portions on the bottomsurfaces of the trenches 60A of the protective thin film 35A areremoved. Accordingly, the bottom surfaces of the trenches 60A areexposed.

Next, as shown in FIG. 7G, by anisotropic deep RIE using the surfaceprotective film 39A as a mask, the bottom surfaces of the trenches 60Aare further dug. Accordingly, at the bottom portions of the trenches60A, exposure spaces 83A from which the crystal face of thesemiconductor substrate 2A is exposed are formed. Subsequent to thisanisotropic deep RIE, by isotropic RIE, reactive ions and etching gasare supplied into the exposure spaces 83A of the trenches 60A. Then, byaction of the reactive ions, etc., the semiconductor substrate 2A isetched in a direction parallel to the surface of the semiconductorsubstrate 2A while being etched in the thickness direction of thesemiconductor substrate 2A from the exposure spaces 83A. Accordingly,all exposure spaces 83A adjacent to each other are integrated togetherto form the cavity 10A inside the semiconductor substrate 2A, and in thecavity 10A, the Z fixed electrode 61A and the Z movable electrode 62Afloat.

Through these steps, the gyro sensor 1A (Z-axis sensor 7A) shown in FIG.1 is obtained.

The first preferred embodiment of the present invention is describedabove, however the present invention can also be carried out in otherembodiments.

For example, as long as the first drive portions 18A and the seconddrive portions 19A engage with each other at an interval, as shown inFIG. 8, they may be arranged so that the first drive portions 18A arealigned like comb teeth and the second drive portions 19A are disposedbetween the comb teeth, or both the first drive portions 18A and thesecond drive portions 19A are aligned like comb teeth.

(2) Second Preferred Embodiment <Entire Arrangement of AccelerationSensor>

FIG. 9 is a schematic plan view of an acceleration sensor according to asecond preferred embodiment of the present invention.

The acceleration sensor 1B includes the semiconductor substrate 2Bhaving a quadrilateral shape in a plan view, a sensor portion 3Bdisposed at the central portion of the semiconductor substrate 2B, andelectrode pads 4B that are disposed on the lateral side of the sensorportion 3B of the semiconductor substrate 2B and for supplying electricpower to the sensor portion 3B.

The sensor portion 3B includes an X-axis sensor 5B, a Y-axis sensor 6B,and Z-axis sensors 7B as sensors that detect accelerations applied indirections along three axes orthogonal to each other in athree-dimensional space. In the present preferred embodiment, the twodirections orthogonal to each other along the surface of thesemiconductor substrate 2B are defined as the X-axis direction and theY-axis direction, and a direction along the thickness direction of thesemiconductor substrate 2B orthogonal to these X-axis and Y-axisdirections is defined as the Z-axis direction.

These three sensors 5B to 7B are covered and sealed by a lid substrate8B by bonding the lid substrate 8B formed of, for example, a siliconsubstrate to the surface of the semiconductor substrate 2B.

A plurality (five in FIG. 9) of the electrode pads 4B are provided ateven intervals.

<Arrangement of X-Axis Sensor and Y-Axis Sensor>

Next, an arrangement of the X-axis sensor and the Y-axis sensor will bedescribed with reference to FIG. 10 to FIG. 12.

FIG. 10 is a schematic plan view of the sensor portion shown in FIG. 9.FIG. 11 is a plan view of a principal portion of the X-axis sensor shownin FIG. 10. FIG. 12 is a sectional view of the principal portion of theX-axis sensor shown in FIG. 10, illustrating a section taken along thecutting plane C-C in FIG. 11.

The semiconductor substrate 2B is formed of a conductive siliconsubstrate (for example, a low-resistance substrate with resistivity of 5Ω·m to 500 Ω·m). This semiconductor substrate 2B has a cavity 10Binside, and in the upper wall 11B (surface portion) of the semiconductorsubstrate 2B having a ceiling that partitions the cavity 10B from thesurface side, the X-axis sensor 5B, the Y-axis sensor 6B, and the Z-axissensors 7B are formed. Specifically, the X-axis sensor 5B, the Y-axissensor 6B, and the Z-axis sensors 7B are formed of portions of thesemiconductor substrate 2B, and are supported while in a floating statewith respect to the bottom wall 12B (back surface portion) of thesemiconductor substrate 2B having a bottom surface that partitions thecavity 10B from the back surface side.

The X-axis sensor 5B and the Y-axis sensor 6B are disposed adjacent toeach other at an interval, and the Z-axis sensors 7B are disposed tosurround the X-axis sensor 5B and the Y-axis sensor 6B, respectively. Inthe present preferred embodiment, the Y-axis sensor 6B has anarrangement that is substantially the same as an arrangement obtained byrotating 90 degrees the X-axis sensor 5B in a plan view. Therefore,hereinafter, instead of a detailed description of the arrangement of theY-axis sensor 6B, in the description of the portions of the X-axissensor 5B, portions of the Y-axis sensor corresponding to the portionsof the X-axis sensor are also described with parentheses.

Between the X-axis sensor 5B and the Z-axis sensor 7B and between theY-axis sensor 6B and the Z-axis sensor 7B, support portions 14B forsupporting these in a floating state are formed. The support portions14B integrally include straight portions 16B extending across the Z-axissensors 7B from one side walls 15B having side surfaces that partitionthe cavity 10B of the semiconductor substrate 2B from the lateral sidestoward the X-axis sensor 5B and the Y-axis sensor 6B, and annularportions 17B surrounding the X-axis sensor 5B and the Y-axis sensor 6B.

The X-axis sensor 5B and the Y-axis sensor 6B are disposed inside theannular portions 17B, and both ends of these sensors are supported attwo points opposing each other on the inner walls of the annularportions 17B. Both ends of the Z-axis sensors 7B are supported on bothside walls of the straight portions 16B.

The X-axis sensor 5B (Y-axis sensor 6B) includes an X fixed electrode21B (Y fixed electrode 41B) fixed to the support portion 14B providedinside the cavity 10B, and an X movable electrode 22B (Y movableelectrode 42B) held to be capable of oscillating with respect to the Xfixed electrode 21B. The X fixed electrode 21B and the X movableelectrode 22B are formed to have the same thickness.

The X fixed electrode 21B (Y fixed electrode 41B) includes a baseportion 23B (base portion 43B of the Y fixed electrode 41B) that isfixed to the support portion 14B and has a quadrilateral annular shapein a plan view, and a plurality of pairs of electrode portions 24B(electrode portions 44B of the Y fixed electrode 41B) aligned like combteeth at even intervals along the inner wall of the base portion 23B.

The X movable electrode 22B (Y movable electrode 42B) includes a baseportion 26B (base portion 46B of the Y movable electrode 42B) thatextends in a direction across the electrode portions 24B of the X fixedelectrode 21B and has both ends connected to the base portion 23B of theX fixed electrode 21B via expandable beam portions 25B (beam portions45B of the Y-axis sensor 6B) along the direction across the electrodeportions 24B, and electrode portions 27B (electrode portions 47B of theY movable electrode 42B) that extend from the base portion 26B to bothsides toward the portions between the electrode portions 24B adjacent toeach other of the X fixed electrode 21B, and are aligned like comb teeththat engage with the electrode portions 24B of the X fixed electrode 21Bwithout contact.

In the X-axis sensor 5B, when the beam portions 25B expand and contractand the base portion 26B of the X movable electrode 22B oscillates alongthe surface of the semiconductor substrate 2B (oscillation Ux), andaccordingly, the electrode portions 27B of the X movable electrode 22Bthat engage with the electrode portions 24B of the X fixed electrode 21Blike comb teeth oscillate alternately in directions approaching and awayfrom the electrode portions 24B of the X fixed electrode 21B.

The base portion 23B of the X fixed electrode 21B has a truss-shapedframed structure including straight main frames extending parallel toeach other and reinforcing frames combined with the main frames so thata triangular space is repeatedly formed along the main frames.

As the electrode portions 24B of the X fixed electrode 21B, twoelectrode portions straight in a plan view that have base end portionsconnected to the base portion 23B and tip end portions thereof opposedto each other are paired, and a plurality of the pairs are provided ateven intervals. Each electrode portion 24B has a framed structure havinga ladder-like shape in a plan view including straight main framesextending parallel to each other and a plurality of traverse frames laidacross the main frames.

The base portion 26B of the X movable electrode 22B is formed by aplurality (six in the present preferred embodiment) of straight framesextending parallel to each other, and both ends of the base portion areconnected to the beam portions 25B. Two beam portions 25B are providedon each of the ends of the base portion 26B of the X movable electrode22B.

Each electrode portion 27B of the X movable electrode 22B has a framedstructure having a ladder-like shape in a plan view including straightmain frames extending parallel to each other across the frames of thebase portion 26B and a plurality of traverse frames laid across the mainframes.

In the X movable electrode 22B, on lines halving the electrode portions27B in a direction orthogonal to the oscillation direction Ux,insulating layers 28B (silicon oxide in the present preferredembodiment) across the traverse frames are embedded from the surface tothe cavity 10B. By the insulating layer 28B, each electrode portion 27Bis insulated and separated into two of one side and the other side alongthe oscillation direction Ux. Accordingly, the separated electrodeportions 27B of the X movable electrode 22B function as independentelectrodes in the X movable electrode 22B.

On the surface of the semiconductor substrate 2B including the X fixedelectrode 21B and the X movable electrode 22B, a first insulating film33B and a second insulating film 34B made of silicon oxide (SiO₂) arelaminated in order.

On this second insulating film 34B, an X first sensor wiring 29B (Yfirst sensor wiring 49B) and an X second sensor wiring 30B (Y secondsensor wiring 50B) are formed.

The X first sensor wiring 29B supplies a drive voltage to one side (inthe present preferred embodiment, the left side on the paper surfaceshown in FIG. 11) of each electrode portion 27B insulated and separatedinto two, and detects a change in voltage accompanying a change incapacitance from the electrode portion 27B. On the other hand, the Xsecond sensor wiring 30B supplies a drive voltage to the other side (inthe present preferred embodiment, the right side on the paper surfaceshown in FIG. 11) of each electrode portion 27B insulated and separatedinto two, and detects a change in voltage accompanying a change incapacitance from the electrode portion 27B.

The X first and X second sensor wirings 29B and 30B are made of aluminum(Al) in the present preferred embodiment. The X first and X secondsensor wirings 29B and 30B are electrically connected to the electrodeportions 27B by penetrating through the first and second insulatingfilms 33B and 34B.

The X first and X second sensor wirings 29B and 30B are led onto thesupport portion 14B via the beam portions 25B of the X movable electrode22B and the base portion 23B of the X fixed electrode 21B, and arepartially exposed as electrode pads 4B. The X first and X second sensorwirings 29B and 30B use the beam portions 25B themselves formed ofportions of the conductive semiconductor substrate 2B as current pathsin sections passing through the beam portions 25B of the X movableelectrode 22B. No aluminum wiring is provided on the beam portions 25B,so that the expandability of the beam portions 25B can be maintained.

To the support portion 14B, an X third sensor wiring 32B that detects achange in voltage caused by a change in capacitance from the electrodeportions 24B of the X fixed electrode 21B is led, and this X thirdsensor wiring 32B is also partially exposed as an electrode pad 4B (notshown) in the same manner as other wirings 29B and 30B.

On the semiconductor substrate 2B, the upper surfaces and the sidesurfaces of the X fixed electrode 21B and the X movable electrode 22Bare coated together with the first insulating film 33B and the secondinsulating film 34B by a protective thin film 35B made of silicon oxide(SiO₂).

On portions except for the cavity 10B of the surface of thesemiconductor substrate 2B, a third insulating film 36B, a fourthinsulating film 37B, a fifth insulating film 38B, and a surfaceprotective film 39B are laminated in order on the second insulating film34B.

In the X-axis sensor 6B structured as described above, when accelerationin the X-axis direction is applied to the X movable electrode 22B, thebeam portions 25B expand and contract and the base portion 26B of the Xmovable electrode 22B oscillates along the surface of the semiconductorsubstrate 2B, and accordingly, the electrode portions 27B of the Xmovable electrode 22B that engage with the electrode portions 24B of theX fixed electrode 21B like comb teeth oscillate alternately indirections approaching and away from the electrode portions 24B of the Xfixed electrode 21B. Accordingly, the opposing distance dx between theelectrode portions 24B of the X fixed electrode 21B and the electrodeportions 27B of the X movable electrode 22B adjacent to each otherchanges. Then, by detecting a change in capacitance between the Xmovable electrode 22B and the X fixed electrode 21B caused by the changein opposing distance dx, the acceleration ax in the X-axis direction isdetected.

In the present preferred embodiment, the acceleration ax in the X-axisdirection is obtained by calculating a difference between detectionvalues of the electrode portions on one side and the other sideinsulated and separated from each other of the X movable electrode 22B.

In the Y-axis sensor 7B, when acceleration in the Y-axis direction isapplied to the Y movable electrode 42B, the beam portions 45B expand andcontract and the base portion 46B of the Y movable electrode 42Boscillates along the surface of the semiconductor substrate 2B, andaccordingly, the electrode portions 47B of the Y movable electrode 42Bthat engage with the electrode portions 44B of the Y fixed electrode 41Blike comb teeth oscillate alternately in directions approaching and awayfrom the electrode portions 44B of the Y fixed electrode 41B.Accordingly, the opposing distance between the electrode portions 44B ofthe Y fixed electrode 41B and the electrode portions 47B of the Ymovable electrode 42B adjacent to each other changes. Then, by detectinga change in capacitance between the Y movable electrode 42B and the Yfixed electrode 41B caused by the change in opposing distance, theacceleration ay in the Y-axis direction is detected.

<Arrangement of Z-Axis Sensor>

Next, with reference to FIG. 10, FIG. 13, and FIG. 14, the arrangementof the Z-axis sensor will be described.

FIG. 13 is a plan view of a principal portion of the Z-axis sensor shownin FIG. 10. FIG. 14 is a sectional view of the principal portion of theZ-axis sensor shown in FIG. 10, illustrating a section taken along thecutting plane D-D in FIG. 13.

Referring to FIG. 10, the semiconductor substrate 2B made of conductivesilicon has the cavity 10B inside as described above. In the upper wall11B (surface portion) of the semiconductor substrate 2B, Z-axis sensors7B supported by the support portions 14B while in a floating state withrespect to the bottom wall 12B of the semiconductor substrate 2B aredisposed to surround the X-axis sensor 5B and the Y-axis sensor 6B,respectively.

Each Z-axis sensor 7B includes a Z fixed electrode 61B as a secondelectrode fixed to the support portion 14B (straight portion 16B)provided inside the cavity 10B, and a Z movable electrode 62B as a firstelectrode held to be capable of oscillating with respect to the Z fixedelectrode 61B. The Z fixed electrode 61B and the Z movable electrode 62Bare formed to have the same thickness.

In one Z-axis sensor 7B of these two Z-axis sensors 7B, the Z movableelectrode 62B is disposed to surround the annular portion 17B of thesupport portion 14B, and the Z fixed electrode 61B is disposed tofurther surround the Z movable electrode 62B. In the other Z-axis sensor7B, the Z fixed electrode 61B is disposed to surround the annularportion 17B of the support portion 14B, and the Z movable electrode 62Bis disposed to further surround the Z fixed electrode 61B. The Z fixedelectrode 61B and the Z movable electrode 62B are connected integrallyto both side walls of the straight portion 16B of the support portion14B.

The Z fixed electrode 61B includes a base portion 63B that has aquadrilateral annular shape in a plan view and is fixed to the supportportion 14B, and electrode portions 64B that are provided on the portionopposite to the straight portion 16B with respect to the X-axis sensor5B (Y-axis sensor 6B) on the base portion 63B and aligned like combteeth.

The Z movable electrode 62B includes a base portion 65B having aquadrilateral annular shape in a plan view, and electrode portions 66Bthat extend from the base portion 65B toward the portions between thecomb-tooth-like electrode portions 64B of the Z fixed electrode 61Badjacent to each other, and are aligned like comb teeth so as to engagewith the electrode portions 64B of the Z fixed electrode 61B withoutcontact. The base portion 65B of this Z movable electrode 62B has atruss-shaped framed structure including straight main frames extendingparallel to each other and reinforcing frames combined with the mainframes so that a triangular space is repeatedly formed along the mainframes. The base portion 65B of the Z movable electrode 62B thusstructured has sections in which the reinforcing frames are omitted atportions on the side opposite to the side of disposition of theelectrode portions 66B, and the main frames in these sections functionas beam portions 67B for enabling the Z movable electrode 62B to move upand down.

Specifically, in this Z-axis sensor 7B, the beam portions 67Belastically warp, and the base portion 65B of the Z movable electrode62B turns like a pendulum in directions approaching and away from thecavity 10B around the beam portions 67B as pivot points (oscillationUz), and accordingly, the electrode portions 66B of the Z movableelectrode 62B that engage with the electrode portions 64B of the Z fixedelectrode 61B like comb teeth oscillate up and down.

The base portion 63B of the Z fixed electrode 61B has a truss-shapedframed structure including straight main frames extending parallel toeach other and reinforcing frames combined with the main frames so thata triangular space is repeatedly formed along the main frames.

The electrode portions 64B of the Z fixed electrode 61B have base endportions connected to the base portion 63B of the Z fixed electrode 61Band tip end portions extending toward the Z movable electrode 62B, andare aligned like comb teeth at even intervals along the inner wall ofthe base portion 63B. In portions close to the base end portions of theelectrode portions 64B, insulating layers 68B (silicon oxide in thepresent preferred embodiment) are embedded from the surface to thecavity 10B across the electrode portions 64B in the width direction. Bythe insulating layers 68B, the electrode portions 64B of the Z fixedelectrode 61B are insulated from other portions of the Z fixed electrode61B.

The electrode portions 66B of the Z movable electrode 62B have base endportions connected to the base portion 65B of the Z movable electrode62B and tip end portions extending toward the portions between theelectrode portions 64B of the Z fixed electrode 61B, and are alignedlike comb teeth engaging with the electrode portions 64B of the Z fixedelectrode 61B without contact. Accordingly, one electrode portion 64B isdisposed on each of one side and the other side in the width directionof each electrode portion 66B.

In portions close to the base end portions of the electrode portions 66Bof the Z movable electrode 62B, insulating layers 74B (silicon oxide inthe present preferred embodiment) are embedded from the surface to thecavity 10B of the semiconductor substrate 2B across the electrodeportions 66B in the width direction. By the insulating layers 74B, theelectrode portions 66B of the Z movable electrode 62B are insulated fromother portions of the Z movable electrode 62B.

In each electrode portion 66B, from the surface of the semiconductorsubstrate 2B to a point halfway in the thickness direction to the cavity10B, a dielectric layer 70B (silicon oxide in the present preferredembodiment) is embedded.

Each dielectric layer 70B is provided one-sided to one end side in thewidth direction of the electrode portion 66B (the right side in adirection from the base end portion toward the tip end portion of eachelectrode portion 66B). Accordingly, each electrode portion 66B ispartitioned into the dielectric layer 70B provided on one end side inthe width direction and a conductive layer 80B provided on the other endside with respect to the dielectric layer 70B (the left side in adirection from the base end portion toward the tip end portion of eachelectrode portion 66B) in a plan view.

The conductive layer 80B is a portion formed by using a portion of thesemiconductor substrate 2B on the electrode portion 66B. The conductivelayer 80B integrally includes a first portion 76B formed adjacently onthe other end side in the width direction to the dielectric layer 70B,and a second portion 78B formed adjacently on the cavity 10B side in thethickness direction to the dielectric layer 70B.

On the surface of the semiconductor substrate 2B including the Z fixedelectrode 61B and the Z movable electrode 62B, as described above, thefirst insulating film 33B and the second insulating film 34B made ofsilicon oxide (SiO₂) are laminated in order.

On the second insulating film 34B, a Z first sensor wiring 75B and a Zsecond sensor wiring 77B are formed. The Z first sensor wiring 75B andthe Z second sensor wiring 77B are respectively connected to theelectrode portions 64B of the Z fixed electrode 61B and the electrodeportions 66B (conductive layers 80B) of the Z movable electrode 62Badjacent to each other.

In detail, the Z first sensor wiring 75B is formed along the baseportion 63B of the Z fixed electrode 61B and includes aluminum wiringsbranched toward the tip end portions of the electrode portions 64Bacross the insulating layers 68B of the electrode portions 64B of the Zfixed electrode 61B. The branched aluminum wirings are electricallyconnected to the tip end sides relative to the insulating layers 68B ofthe electrode portions 64B by penetrating through the first insulatingfilm 33B and the second insulating film 34B. As shown in FIG. 10, the Zfirst sensor wiring 75B is led onto the support portion 14B via the baseportion 63B of the Z fixed electrode 61B, and partially exposed aselectrode pads 4B.

The Z second sensor wiring 77B is formed along the base portion 65B ofthe Z movable electrode 62B, and includes aluminum wirings branchedtoward the electrode portions 66B across the insulating layers 74B closeto the base end portions of the electrode portions 66B of the Z movableelectrode 62B. The branched aluminum wirings are electrically connectedto the electrode portions 66B by penetrating through the firstinsulating film 33B and the second insulating film 34B. As shown in FIG.10, the Z second sensor wiring 77B is led onto the support portion 14Bvia the base portion 65B of the Z movable electrode 62B, and partiallyexposed as electrode pads 4B.

On the semiconductor substrate 2B, the upper surfaces and side surfacesof the Z fixed electrode 61B and the Z movable electrode 62B are coatedtogether with the first insulating film 33B and the second insulatingfilm 34B by a protective thin film 35B made of silicon oxide (SiO₂).

On portions other than the cavity 10B on the surface of thesemiconductor substrate 2B, the third insulating film 36B, the fourthinsulating film 37B, the fifth insulating film 38B, and the surfaceprotective film 39B are laminated in order on the second insulating film34B.

In this Z-axis sensor 7B, the electrode portions 64B to which the Zfirst sensor wiring 75B is connected and the conductive layers 80B ofthe electrode portions 66B to which the Z second sensor wiring 77B isconnected are opposed to each other, and constitute electrodes of acapacitor when a fixed voltage is applied between these electrodes andthe capacitance changes due to a change in opposing area S.

When acceleration in the Z-axis direction is applied to the Z movableelectrode 62B, the comb-tooth-like Z movable electrode 62B oscillates upand down like a pendulum similarly around the comb-tooth-like Z fixedelectrode 61B as a center of oscillation along the Z-axis direction withrespect to the Z fixed electrode 61B. Accordingly, the opposing area Sbetween the electrode portions 64B of the Z fixed electrode 61B and theelectrode portions 66B of the Z movable electrode 62B adjacent to eachother changes. Then, by detecting a change in capacitance between the Zmovable electrode 62B and the Z fixed electrode 61B caused by the changein opposing area S, the acceleration az in the Z-axis direction isdetected.

In the present preferred embodiment, the conductive layer 80B of eachelectrode portion 66B includes a first portion 76B opposed to theelectrode portion 64B of the Z fixed electrode 61B via the dielectriclayer 70B and a second portion 78B opposed to the electrode portion 64Bwithout interposition of the dielectric layer 70B therebetween.

Therefore, in the capacitor arranged by making the electrode portions64B of the Z fixed electrode 61B and the electrode portions 66B of the Zmovable electrode 62B opposed to each other, at the portion at which thefirst portion 76B of the conductive layer 80B and the electrode portion64B are opposed to each other, the electrode-to-electrode distance d1 ofthe capacitor is larger by the width W of the dielectric layer 70B thanthe electrode-to-electrode distance d2 that the capacitor originally has(the distance between the second portion 78B of the conductive layer 80Band the electrode portion 64B of the Z fixed electrode 61B) (that is,d1=d2+W). Therefore, in the same capacitor, a capacitance difference canbe provided.

Therefore, when the Z movable electrode 62B oscillates first to the side(upper side) away from the cavity 10B with respect to the Z fixedelectrode 61B, the capacitance of the capacitor decreases at a decreaserate D1 (D1>0) based on the electrode-to-electrode distance d1 while thefirst portions 76B of the conductive layers 80B are opposed to theelectrode portions 64B of the Z fixed electrode 61B. Thereafter, whenthe first portions 76B completely protrude above the Z fixed electrode61B and only the second portions 78B of the conductive layers 80B areopposed to the electrode portions 64B of the Z fixed electrode 61B, thecapacitance decreases from this timing at a decrease rate D2 (D2>0)based on the original electrode-to-electrode distance d2.

This decrease rate D2 of the capacitance is larger than the decreaserate D1 because the electrode-to-electrode distance d2 is smaller thanthe electrode-to-electrode distance d1 and the capacitance to decreaseper unit time increases. Specifically, when the Z movable electrode 62Bstarts to oscillate to the upper side, the capacitance of the capacitordecreases at the first decrease rate D1 and then decreases at the seconddecrease rate D2 higher than the first decrease rate D1.

On the other hand, when the Z movable electrode 62B oscillates first tothe side (lower side) to approach the cavity 10B with respect to the Zfixed electrode 61B, the capacitance of the capacitor decreases at thedecrease rate D2 based on the electrode-to-electrode distance d2 untilthe second portions 78B completely protrude below the Z fixed electrode61B. Thereafter, when the second portions 78B completely protrude belowthe Z fixed electrode 61B and only the first portions 76B are opposed tothe electrode portions 64B of the Z fixed electrode 61B, the capacitancedecreases from this timing at the decrease rate D1 based on theelectrode-to-electrode distance d1. This decrease rate D1 of thecapacitance is smaller than the decrease rate D2 because theelectrode-to-electrode distance d1 is larger than theelectrode-to-electrode distance d2 and the capacitance to decrease perunit time becomes smaller. Specifically, when the Z movable electrode62B starts to oscillate to the lower side, the capacitance of thecapacitor decreases at the second decrease rate D2 and then decreases atthe first decrease rate D1 smaller than the second decrease rate D2.

Therefore, by detecting whether the capacitance of the capacitordecreases at the relatively small decrease rate D1 and then decreases atthe relatively large decrease rate D2 (D1->D2) or decreases at therelatively large decrease rate D2 and then decreases at the relativelysmall decrease rate D1 (D2->D1), the direction in which the Z movableelectrode 62B oscillated first (the direction away from the cavity 10Bor the direction approaching the cavity 10B) can be easily grasped. As aresult, the direction of the acceleration vector can be accuratelydetected, so that the detection sensitivity can be improved.

In addition, in the present preferred embodiment, each conductive layer80B integrally includes the first portion 76B and the second portion78B, and therefore, the conductive layers 80B are formed in the entirethickness direction from the surface to the back surface of the Zmovable electrode 62B. Therefore, regardless of the direction ofoscillation (upward or downward) of the Z movable electrode 62B withrespect to the Z fixed electrode 61B, the opposing area S between theconductive layers 80B of the Z movable electrode 62B and the Z fixedelectrode 61B decreases by necessity. In detail, when the Z movableelectrode 62B oscillates to the upper side first, the opposing areabetween the first portions 76B of the conductive layers 80B and theelectrode portions 64B of the Z fixed electrode 61B decreases, and onthe other hand, when the Z movable electrode oscillates to the lowerside first, the opposing area between the second portions 78B of theconductive layers 80B and the electrode portions 64B of the Z fixedelectrode 61B decreases.

Accordingly, a change in capacitance can be detected immediately afterthe start of oscillation of the Z movable electrode 62B, so that themagnitude of the acceleration vector immediately after the start ofoscillation can also be detected.

This improvement in detection sensitivity is obtained by embedding thedielectric layers 70B in the electrode portions 66B of the Z movableelectrode 62B constituting the capacitor, so that the sensor structurecan be prevented from becoming complicated.

Further, the semiconductor substrate 2B is a conductive siliconsubstrate, so that even without applying a special treatment for givingconductivity to the X fixed electrode 21B, the Y fixed electrode 41B,and the Z fixed electrode 61B, and the X movable electrode 22B, the Ymovable electrode 42B, and the Z movable electrode 62B molded intopredetermined shapes, the molded structures can be used as they are aselectrodes. In addition, the portions except for the portions to be usedas electrodes can be used as wirings (the Z first sensor wiring 75B, theZ second sensor wiring 77B, etc.).

In the present preferred embodiment, the acceleration az in the Z-axisdirection can be obtained by calculating a difference between adetection value of the Z-axis sensor 7B surrounding the X-axis sensor 5Band a detection value of the Z-axis sensor 7B surrounding the Y-axissensor 6B. For example, as shown in FIG. 10, the difference can beobtained by making the position relationship of the fixed electrode andthe movable electrode of the Z-axis sensor 7B surrounding the X-axissensor 5B opposite to the position relationship of the fixed electrodeand the movable electrode of the Z-axis sensor 7B surrounding the Y-axissensor 6B. Accordingly, the manner of oscillation of the Z movableelectrode 62B differs between the pair of Z-axis sensors 7B, so that thedifference occurs.

<Method for Manufacturing Acceleration Sensor 1B>

Next, the manufacturing process of the above-described accelerationsensor 1B will be described in order of steps with reference to FIG. 15Ato FIG. 15G. In this paragraph, only the manufacturing process of theZ-axis sensors is shown in the drawings, and the manufacturing processesof the X-axis sensor and the Y-axis sensor are omitted, however, themanufacturing processes of the X-axis sensor and the Y-axis sensor areperformed in parallel to the manufacturing process of the Z-axis sensorsin the same manner as the manufacturing process of the Z-axis sensors.

FIG. 15A to FIG. 15G are schematic sectional views showing parts of themanufacturing process of the acceleration sensor 1B according to thesecond preferred embodiment of the present invention in order of steps,illustrating a section taken along the cutting plane at the sameposition as in FIG. 14.

To manufacture this acceleration sensor 1B, first, as shown in FIG. 15A,the surface of the semiconductor substrate 2B made of conductive siliconis thermally oxidized (for example, temperature: 1100 to 1200° C., filmthickness: 5000 Å). Accordingly, the first insulating film 33B is formedon the surface of the semiconductor substrate 2B. Next, by a knownpatterning technique, the first insulating film 33B is patterned, andopenings in which the dielectric layers 70B and the insulating layers68B and 74B should be embedded are formed. Next, by anisotropic deep RIE(Reactive Ion Etching) using the first insulating film 33B as a hardmask, specifically, by a Bosch process, the semiconductor substrate 2Bis dug. Accordingly, trenches are formed in the semiconductor substrate2B. In the Bosch process, a step of etching the semiconductor substrate2B by using SF₆ (sulfur hexafluoride) and a step of forming a protectivefilm on the etched surfaces by using C₄F₈ (perfluorocyclobutane) arealternately repeated. Accordingly, the semiconductor substrate 2B can beetched at a high aspect ratio, however, a wavy irregularity calledscallop is formed on the etched surfaces (inner peripheral surfaces ofthe trenches). Subsequently, the insides of the trenches formed in thesemiconductor substrate 2B and the surface of the semiconductorsubstrate 2B are thermally oxidized (for example, temperature: 1100 to1200° C.), and then, the surface of the oxide film is etched back (forexample, the film thickness after etching back is 21800 Å). Accordingly,the dielectric layers 70B and the insulating layers 68B and 74B fillingthe trenches are formed concurrently (only the dielectric layers 70B andthe insulating layer 74B are shown).

Next, as shown in FIG. 15B, by a CVD method, the second insulating film34B made of silicon oxide is laminated on the semiconductor substrate2B. Next, the second insulating film 34B and the first insulating film33B are successively etched. Accordingly, contact holes are formed inthe second insulating film 34B and the first insulating film 33B. Next,contact plugs filling the contact holes are formed, and by sputtering,aluminum is deposited (for example, 7000 Å) on the second insulatingfilm 34B, and the aluminum deposit layer is patterned. Accordingly, thewirings 75B and 77B are formed on the second insulating film 34B.

Next, as shown in FIG. 15C, by a CVD method, the third insulating film36B, the fourth insulating film 37B, the fifth insulating film 38B, andthe surface protective film 39B are laminated in order on the secondinsulating film 34B. Next, the third to fifth insulating films 36B to38B and the surface protective film 39B on the region in which thecavity 10B of the semiconductor substrate 2B should be formed areremoved by etching.

Next, as shown in FIG. 15D, a resist having openings in regions otherthan the regions in which the Z fixed electrode 61B and the Z movableelectrode 62B should be formed is formed on the second insulating film34B. Subsequently, by anisotropic deep RIE using this resist as a mask,specifically, by a Bosch process, the semiconductor substrate 2B is dug.Accordingly, the surface portion of the semiconductor substrate 2B ismolded into the shapes of the Z fixed electrode 61B and the Z movableelectrode 62B, and between these, trenches 60B are formed. In the Boschprocess, a step of etching the semiconductor substrate 2B by using SF₆(sulfur hexafluoride) and a step of forming a protective film on theetched surfaces by using C₄F₈ (perfluorocyclobutane) are alternatelyrepeated. After the deep RIE, the resist is stripped.

Next, as shown in FIG. 15E, by thermal oxidization or by a PECVD method,on the entire surfaces of the Z fixed electrode 61B and the Z movableelectrode 62B and the entire inner surfaces of the trenches 60B (thatis, the side surfaces and the bottom surfaces that define the trenches60B), the protective thin film 35B made of silicon oxide (SiO₂) isformed.

Next, as shown in FIG. 15F, by etching back, the portions on the bottomsurfaces of the trenches 60B of the protective thin film 35B areremoved. Accordingly, the bottom surfaces of the trenches 60B areexposed.

Next, as shown in FIG. 15G, by anisotropic deep RIE using the surfaceprotective film 39B as a mask, the bottom surfaces of the trenches 60Bare further dug. Accordingly, at the bottom portions of the trenches60B, exposure spaces 83B from which the crystal face of thesemiconductor substrate 2B is exposed are formed. Subsequent to thisanisotropic deep RIE, by isotropic RIE, reactive ions and etching gasare supplied into the exposure spaces 83B of the trenches 60B. Then, byaction of the reactive ions, etc., the semiconductor substrate 2B isetched in a direction parallel to the surface of the semiconductorsubstrate 2B while being etched in the thickness direction of thesemiconductor substrate 2B from the exposure spaces 83B. Accordingly,all exposure spaces 83B adjacent to each other are integrated togetherto form the cavity 10B inside the semiconductor substrate 2B, and insidethe cavity 10B, the Z fixed electrode 61B and the Z movable electrode62B float.

Through these steps, the acceleration sensor 1B (Z-axis sensor 7B) shownin FIG. 9 is obtained.

The second preferred embodiment of the present invention is describedabove, however the present invention can also be carried out in otherembodiments.

For example, as shown in FIG. 16, each electrode portion 66B of the Zmovable electrode 62B may have a lamination structure including adielectric layer 81B formed from one end to the other end in the widthdirection of the electrode portion 66B and a conductive layer 82B formedbelow the dielectric layer 81B.

With the present arrangement, the portion from the surface or the backsurface to a halfway point of the Z movable electrode 62B is entirelyformed of the dielectric layer 81B. In this case, in the capacitorformed by making the electrode portions 64B of the Z fixed electrode 61Band the electrode portions 66B of the Z movable electrode 62B opposed toeach other, at the portions at which the dielectric layers 81B and theelectrode portions 64B of the Z fixed electrode 61B are opposed to eachother, no conductive layer opposed to the Z fixed electrode 61B isprovided, so that the capacitance becomes 0 (zero).

Therefore, when the Z movable electrode 62B oscillates first to the side(upper side) away from the cavity 10B with respect to the Z fixedelectrode 61B, the capacitance of the capacitor does not change (thatis, the decrease rate D1=0) while the dielectric layers 81B are opposedto the electrode portions 64B of the Z fixed electrode 61B. Thereafter,when the dielectric layers 81B completely protrude above the Z fixedelectrode 61B and only the conductive layers 82B are opposed to the Zfixed electrode 61B, the capacitance decreases from this timing at thedecrease rate D2 (D2>0) based on the original electrode-to-electrodedistance d2.

On the other hand, when the Z movable electrode 62B oscillates first tothe side (lower side) to approach the cavity 10B, the capacitance of thecapacitor decreases at the decrease rate D2 based on theelectrode-to-electrode distance d2 while the conductive layers 82B areopposed to the electrode portions 64B of the Z fixed electrode 61B.Thereafter, when the conductive layers 82B completely protrude below theZ fixed electrode 61B and only the dielectric layers 81B are opposed tothe Z fixed electrode 61B, the capacitance does not change from thistiming (that is, the decrease rate D1=0).

Therefore, with the present arrangement, the direction of theacceleration vector can be judged based on whether the decrease rate ofthe capacitance is 0 or not, that is, whether the capacitance changes ornot. Accordingly, the acceleration can be easily detected.

The dielectric layers 70B and 81B may be made of a material other thansilicon oxide as long as the material is dielectric.

The dielectric layers 70B may be provided in the Z fixed electrode 61Bas shown in FIG. 17 instead of in the Z movable electrode 62B.Similarly, the dielectric layers 81B may also be provided in the Z fixedelectrode 61B as shown in FIG. 18 instead of in the Z movable electrode62B.

(3) Third Preferred Embodiment <Entire Arrangement of MEMS Package>

FIG. 19 is a schematic perspective view of a MEMS package according to athird preferred embodiment of the present invention. FIG. 20 is asectional view of a principal portion of the MEMS package shown in FIG.19, illustrating a section taken along the cutting plane E-E in FIG. 19.

The MEMS package 1C includes a substrate 2C, an acceleration sensor 3Cas a MEMS sensor, external terminals 4C, an integrated circuit 5C (ASIC:Application Specific Integrated Circuit), and a resin package 6C.

The substrate 2C is formed to have a rectangular plate shape having asurface 7C and a back surface 8C.

The acceleration sensor 3C is disposed on one end portion in thelongitudinal direction on the surface 7C side of the substrate 2C. Theacceleration sensor 3C includes abase substrate 9C as a semiconductorsubstrate formed of a Si substrate having a square plate shape.

The base substrate 9C has a sensor region 10C and a pad region 11C(peripheral region) surrounding the sensor region 10C.

In the sensor region 10C, as sensors that detect respectiveaccelerations around three axes orthogonal to each other in athree-dimensional space, an X-axis sensor 12C, a Y-axis sensor 13C, andZ-axis sensors 14C are provided. In the present preferred embodiment,the two directions orthogonal to each other along the surface 7C of thesubstrate 2C are defined as the X-axis direction and the Y-axisdirection, and a direction along the thickness direction of thesubstrate 2C orthogonal to these X-axis and Y-axis directions is definedas the Z-axis direction.

In the pad region 11C, electrode pads 15C for supplying voltages to theX-axis sensor 12C, the Y-axis sensor 13C, and the Z-axis sensor 14C,respectively, are formed. A plurality (seven in FIG. 19) of electrodepads 15C are provided at even intervals along the width directionorthogonal to the longitudinal direction of the substrate 2C.

The sensor region 10C and the pad region 11C are covered by a protectivelayer 16C made of SiO₂ as a first inorganic material and formed on thebase substrate 9C.

The protective layer 16C is formed to have a mesa shape integrallyincluding a flat top portion 18C (central portion) opposed to the sensorregion 10C via a space 17C, a flat bottom portion 19C (peripheral edgeportion) surrounding the top portion 18C and bonded to the pad region11C, and an inclined portion 20C inclined from the entire circumferenceof the peripheral edge of the top portion 18C toward the bottom portion19C. Between the top portion 18C and the bottom portion 19C of theprotective layer 16C, a level difference with a predetermined height Lis provided.

In the top portion 18C of the protective layer 16C, a large number ofthrough holes 21C that make communication between the inside and theoutside of the space 17C are formed in a matrix.

On the bottom portion 19C of the protective layer 16C, pad openings 22Cfor exposing the respective electrode pads 15C are formed as many as theelectrode pads 15C. In the present preferred embodiment, the arrangementin which the bottom portion 19C of the protective layer 16C is bonded tothe pad region 11C includes an idea that the bottom portion 19C of theprotective layer 16C is in close contact with the surface of the basesubstrate 9C (meaning the uppermost surface of the base substrate 9C,and meaning the uppermost surface of an insulating film when theinsulating film such as a surface protective film is formed on the basesubstrate 9C).

A plurality (twelve in FIG. 19) of the external terminals 4C areprovided at even intervals along the width direction of the substrate 2Con the other end portion in the longitudinal direction of the substrate2C (the end portion on the side opposite to the acceleration sensor 3C).Each external terminal 4C is formed to penetrate through the substrate2C in the thickness direction, and is exposed as an internal pad 23C tothe surface 7C of the substrate 2C, and exposed as an external pad 24Cto the back surface 8C of the substrate 2C.

The integrated circuit 5C is disposed between the acceleration sensor 3Cand the external terminals 4C (internal pads 23C) on the surface 7C sideof the substrate 2C. The integrated circuit 5C is formed of, forexample, a Si substrate having a rectangular plate shape long in thewidth direction of the substrate 2C. Inside the Si substrate, chargeamplifiers that amplify electric signals output from the sensors 12C to14C, filter circuits (low-pass filter: LPF, etc.) that extract specificfrequency components of the electric signals, and logic circuits thatcarry out logic operations of filtered electric signals, etc., areformed. These circuits consist of, for example, CMOS devices. Theintegrated circuit 5C includes first electrode pads 25C and secondelectrode pads 26C.

A plurality (seven in FIG. 19) of the first electrode pads 25C areprovided at even intervals along the width direction of the substrate 2Con the end portion on the side close to the acceleration sensor 3C inthe longitudinal direction of the substrate 2C. The first electrode pads25C are connected one-to-one to the electrode pads 15C of theacceleration sensor 3C by bonding wires 27C.

A plurality (twelve in FIG. 19) of the second electrode pads 26C areprovided at even intervals along the width direction of the substrate 2Con an end portion on the side close to the external terminals 4C in thelongitudinal direction of the substrate 2C. The second electrode pads26C are connected one-to-one to the internal pads 23C of the externalterminals 4C by bonding wires 28C.

The resin package 6C defines the external shape of the MEMS package 1Cin cooperation with the substrate 2C, and is formed to have asubstantially rectangular parallelepiped shape. The resin package 6C ismade of, for example, a known molding resin such as epoxy resin, andseals the acceleration sensor 3C and the integrated circuit 5C so as tocover the bonding wires 27C and 28C and the internal pads 23C as well asthe acceleration sensor 3C and the integrated circuit 5C, and expose theexternal pads 24C.

<Arrangement of X-Axis Sensor and Y-Axis Sensor>

Next, with reference to FIG. 21 to FIG. 23, the arrangement of theX-axis sensor and the Y-axis sensor will be described.

FIG. 21 is a schematic plan view of the acceleration sensor shown inFIG. 19. FIG. 22 is a plan view of a principal portion of the X-axissensor shown in FIG. 21. FIG. 23 is a sectional view of a principalportion of the X-axis sensor shown in FIG. 21, illustrating a sectiontaken along the cutting plane F-F in FIG. 22.

The acceleration sensor 3C includes the base substrate 9C formed of a Sisubstrate as described above. This base substrate 9C has a cavity 29Cinside, and in the upper wall 30C as a surface layer portion of the basesubstrate 9C having a ceiling that partitions the cavity 29C from thesurface side, the X-axis sensor 12C, the Y-axis sensor 13C, and theZ-axis sensors 14C are formed. Specifically, the X-axis sensor 12C, theY-axis sensor 13C, and the Z-axis sensors 14C are formed of portions ofthe base substrate 9C, and are supported while in a floating state withrespect to the bottom wall 31C of the base substrate 9C that has abottom surface partitioning the cavity 29C from the back surface side.

The X-axis sensor 12C and the Y-axis sensor 13C are disposed adjacent toeach other at an interval. The Z-axis sensors 14C are disposed tosurround the X-axis sensor 12C and the Y-axis sensor 13C, respectively.

In the present preferred embodiment, the Y-axis sensor 13C has anarrangement that is substantially the same as an arrangement obtained byrotating 90 degrees the X-axis sensor 12C in a plan view. Therefore,hereinafter, instead of a detailed description of the arrangement of theY-axis sensor 13C, in the description of the portions of the X-axissensor 12C, portions of the Y-axis sensor corresponding to the portionsof the X-axis sensor are also described with parentheses.

Between the X-axis sensor 12C and the Z-axis sensor 14C and between theY-axis sensor 13C and the Z-axis sensor 14C, support portions 32C forsupporting these sensors in a floating state are formed.

The support portions 32C integrally include straight portions 34Cextending across the Z-axis sensors 14C toward the X-axis sensor 12C andthe Y-axis sensor 13C from one side wall 33C having side surfacespartitioning the cavity 29C of the base substrate 9C from the lateralsides, and annular portions 35C surrounding the X-axis sensor 12C andthe Y-axis sensor 13C.

The X-axis sensor 12C and the Y-axis sensor 13C are disposed inside theannular portions 35C, and both ends of these sensors are supported attwo points opposing each other on the inner walls of the annularportions 35C. Both ends of the Z-axis sensors 14C are supported by bothside walls of the straight portions 34C.

The X-axis sensor 12C (Y-axis sensor 13C) has an X fixed electrode 41C(Y fixed electrode 61C) and an X movable electrode 42C (Y movableelectrode 62C) that are formed to have the same thickness with respectto each other.

The X fixed electrode 41C (Y fixed electrode 61C) includes a first baseportion 43C (first base portion 63C of the Y fixed electrode 61C) havinga quadrilateral annular shape in a plan view fixed to the supportportion 32C, and a plurality of pairs of first comb tooth portions 44C(first comb tooth portions 64C of the Y fixed electrode 61C) alignedlike comb teeth at even intervals along the inner wall of the first baseportion 43C.

The first base portion 43C of the X fixed electrode 41C has atruss-shaped framed structure including straight main frames extendingparallel to each other and reinforcing frames combined with the mainframes so that a triangular space is repeatedly formed along the mainframes.

As the first comb tooth portions 44C of the X fixed electrode 41C, twoelectrode portions straight in a plan view and having base end portionsconnected to the first base portion 43C and tip end portions thereofopposed to each other are paired, and a plurality of pairs of theelectrode portions are provided at even intervals. Each first comb toothportion 44C has a framed structure that has a ladder-like shape in aplan view and includes straight main frames extending parallel to eachother and a plurality of traverse frames laid across the main frames.

The X movable electrode 42C (Y movable electrode 62C) is held to becapable of oscillating with respect to the X fixed electrode 41C.

The X movable electrode 42C (Y movable electrode 62C) includes a secondbase portion 45C (second base portion 65C of the Y movable electrode62C) and second comb tooth portions 46C (second comb tooth portions 66Cof the Y movable electrode 62C).

The second base portion 45C of the X movable electrode 42C is formed ofa plurality (six in the present preferred embodiment) of straight framesextending parallel to each other along a direction across the first combtooth portions 44C of the X fixed electrode 41C. Both ends of the secondbase portion 45C are connected to beam portions 47C (beam portions 67Cof the Y movable electrode 62C) capable of expanding and contractingalong the direction across the first comb tooth portions 44C.

Two beam portions 47C are provided on each of the ends of the secondbase portion 45C of the X movable electrode 42C.

The second comb tooth portions 46C of the X movable electrode 42C extendfrom the second base portion 45C to both sides toward the portionsbetween the first comb tooth portions 44C of the X fixed electrode 41Cadjacent to each other, and are aligned like comb teeth that engage withthe first comb tooth portions 44C of the X fixed electrode 41C withoutcontact therebetween. Each second comb tooth portion 46C has a framedstructure having a ladder-like shape in a plan view including straightmain frames extending parallel to each other across the frames of thesecond base portion 45C and a plurality of traverse frames laid acrossthe main frames.

In the X movable electrode 42C, on lines halving the second comb toothportions 46C in a direction orthogonal to the oscillation direction Ux,insulating layers 48C across the traverse frames are embedded from thesurface to the cavity 29C.

The insulating layers 48C are made of SiO₂ (silicon oxide). Each secondcomb tooth portion 46C is insulated and separated into two of one sideand the other side along the oscillation direction Ux by the insulatinglayers 48C. Accordingly, the separated second comb tooth portions 46C ofthe X movable electrode 42C function as respective independentelectrodes in the X movable electrode 42C.

On the surface of the base substrate 9C including the X fixed electrode41C and the X movable electrode 42C, a first insulating film 49C and asecond insulating film 50C made of silicon oxide (SiO₂) are laminated inorder.

Between the first insulating film 49C and the second insulating film50C, an X first detection wiring 51C (Y first detection wiring 71C) andan X second detection wiring 52C (Y second detection wiring 72C) areformed.

The X first detection wiring 51C detects a change in voltageaccompanying a change in capacitance from one side (in the presentpreferred embodiment, the left side on the paper surface shown in FIG.21) of each second comb tooth portion 46C insulated and separated intotwo.

The X second detection wiring 52C detects a change in voltageaccompanying a change in capacitance from the other side (in the presentpreferred embodiment, the right side on the paper surface shown in FIG.21) of each second comb tooth portion 46C insulated and separated intotwo.

The X first detection wiring 51C and the X second detection wiring 52Care made of aluminum (Al) in the present preferred embodiment. The Xfirst detection wiring 51C and the X second detection wiring 52C areelectrically connected to the second comb tooth portions 46C bypenetrating through the first insulating film 49C.

The X first detection wiring 51C and the X second detection wiring 52Care led onto the support portion 32C via the beam portions 47C of the Xmovable electrode 42C and the first base portion 43C of the X fixedelectrode 41C, and partially exposed as electrode pads 15C.

The X first detection wiring 51C and the X second detection wiring 52Cuse the beam portions 47C themselves formed of portions of theconductive base substrate 9C as current paths in sections passingthrough the beam portions 47C of the respective X movable electrode 42C.No aluminum wiring is provided on the beam portions 47C, so that theexpandability of the beam portions 47C can be maintained.

To the support portion 32C, an X third detection wiring 53C (Y thirddetection wiring 73C) that detects a change in voltage accompanying achange in capacitance from the first comb tooth portions 44C of the Xfixed electrode 41C is led. The X third detection wiring 53C is alsopartially exposed as an electrode pad 15C (not shown) in the same manneras other wirings 51C and 52C.

The upper surfaces and side surfaces of the X fixed electrode 41C andthe X movable electrode 42C are coated by a protective thin film 54Cmade of SiO₂ so that the first insulating film 49C and the secondinsulating film 50C are covered.

In the X-axis sensor 12C structured as described above, the first combtooth portions 44C (X fixed electrode 41C) to which the X thirddetection wiring 53C is connected and the second comb tooth portions 46C(X movable electrode 42C) to which the X first detection wiring 51C andthe X second detection wiring 52C are connected are opposed to eachother at an electrode-to-electrode distance d_(x) to constitute acapacitor.

Then, when acceleration in the X-axis direction is applied to the Xmovable electrode 42C, the beam portions 47C expand and contract and thesecond base portion 45C of the X movable electrode 42C oscillates alongthe surface of the base substrate 9C. Accordingly, the second comb toothportions 46C of the X movable electrode 42C that engage with the firstcomb tooth portions 44C of the X fixed electrode 41C like comb teethoscillate alternately in directions approaching and away from the firstcomb tooth portions 44C of the X fixed electrode 41C.

As a result, the electrode-to-electrode distance d_(x) between the firstcomb tooth portions 44C of the X fixed electrode 41C and the second combtooth portions 46C of the X movable electrode 42C adjacent to each otherchanges. Then, by detecting a change in capacitance between the Xmovable electrode 42C and the X fixed electrode 41C caused by the changein electrode-to-electrode distance d_(x), the acceleration a_(x) in theX-axis direction is detected.

In the present preferred embodiment, the acceleration a_(x) in theX-axis direction is obtained by calculating a difference betweendetection values of one side and the other side electrode portionsinsulated and separated from each other of the X movable electrode 42C.

In the Y-axis sensor 13C, when acceleration in the Y-axis direction isapplied to the Y movable electrode 62C, the beam portions 67C expand andcontract and the second base portion 65C of the Y movable electrode 62Coscillates along the surface of the base substrate 9C. Accordingly, thesecond comb tooth portions 66C of the Y movable electrode 62C thatengage with the first comb tooth portions 64C of the Y fixed electrode61C like comb teeth oscillate alternately in directions approaching andaway from the first comb tooth portions 64C of the Y fixed electrode61C.

As a result, the electrode-to-electrode distance d_(y) between the firstcomb tooth portions 64C of the Y fixed electrode 61C and the second combtooth portions 66C of the Y movable electrode 62C adjacent to each otherchanges. Then, by detecting a change in capacitance between the Ymovable electrode 62C and the Y fixed electrode 61C caused by the changein electrode-to-electrode distance d_(y), the acceleration a_(y) in theY-axis direction is detected.

<Arrangement of Z-Axis Sensor>

Next, an arrangement of the Z-axis sensor will be described withreference to FIG. 21, FIG. 24, and FIG. 25.

FIG. 24 is a plan view of a principal portion of the Z-axis sensor shownin FIG. 21. FIG. 25 is a sectional view of the principal portion of theZ-axis sensor shown in FIG. 21, illustrating a section taken along thecutting plane G-G in FIG. 24.

The Z-axis sensors 14C are disposed to surround the X-axis sensor 12Cand the Y-axis sensor 13C, respectively, as described above.

The Z-axis sensor 14C includes a Z fixed electrode 81C and a Z movableelectrode 82C formed to have the same thickness and the same width withrespect to each other. In FIG. 24 and FIG. 25, the thickness and thewidth of the Z fixed electrode 81C are the thickness T₁ and the widthW₁, respectively, and the thickness and the width of the Z movableelectrode 82C are the thickness T₂ and the width W₂, respectively.

The Z fixed electrode 81C is fixed to the support portion 32C (straightportion 34C) provided inside the cavity 29C.

The Z movable electrode 82C is held to be capable of oscillating withrespect to the Z fixed electrode 81C.

In the present preferred embodiment, in one Z-axis sensor 14C of the twoZ-axis sensors 14C, the Z movable electrode 82C is disposed to surroundthe annular portion 35C, and the Z fixed electrode 81C is disposed tosurround the Z movable electrode 82C.

In the other Z-axis sensor 14C, the Z fixed electrode 81C is disposed tosurround the annular portion 35C, and the Z movable electrode 82C isdisposed to surround the Z fixed electrode 81C.

In each Z-axis sensor 14C, the Z fixed electrode 81C includes a firstbase portion 83C and a plurality of first comb tooth portions 84C.

The first base portion 83C of the Z fixed electrode 81C is formed tohave a quadrilateral annular shape in a plan view and fixed to thesupport portion 32C. The first base portion 83C has a truss-shapedframed structure including straight main frames extending parallel toeach other and reinforcing frames combined with the main frames so thata triangular space is repeatedly formed along the main frames.

The first comb tooth portions 84C of the Z fixed electrode 81C arealigned like comb teeth at even intervals along the inner wall of thefirst base portion 83C on the portion on the side opposite to thestraight portion 34C with respect to the X-axis sensor 12C (Y-axissensor 13C) in the first base portion 83C.

The first comb tooth portions 84C have base end portions connected tothe first base portion 83C of the Z fixed electrode 81C, and tip endportions extending toward the Z movable electrode 82C. In portions closeto the base end portions of the first comb tooth portions 84C,insulating layers 85C as first insulating layers across the first combtooth portions 84C in the width direction are embedded from the surfaceto the cavity 29C.

The insulating layers 85C are made of SiO₂. The first comb toothportions 84C are insulated from other portions of the Z fixed electrode81C by the insulating layers 85C.

In each Z-axis sensor 14C, the Z movable electrode 82C includes a secondbase portion 86C and second comb tooth portions 87C.

The second base portion 86C of the Z movable electrode 82C is formed tohave a quadrilateral annular shape in a plan view. In addition, thesecond base portion 86C has a truss-shaped framed structure includingstraight main frames extending parallel to each other and reinforcingframes combined with the main frames so that a triangular space isrepeatedly formed along the main frames.

The second base portion 86C having the framed structure has sections inwhich the reinforcing frames are omitted at portions on the sideopposite to the disposition of the second comb tooth portions 87C. Themain frames in these omitted sections function as beam portions 88C forenabling the Z movable electrode 82C to move up and down.

The second comb tooth portions 87C of the Z movable electrode 82C extendfrom the second base portion 86C toward the portions between the firstcomb tooth portions 84C adjacent to each other of the Z fixed electrode81C, and aligned like comb teeth to engage with the first comb toothportions 84C without contact.

The second comb tooth portions 87C have base end portions connected tothe second base portion 86C of the Z movable electrode 82C, and tip endportions extending toward the portions between the first comb toothportions 84C of the Z fixed electrode 81C.

In portions close to the base end portions of the second comb toothportions 87C, insulating layers 89C as second insulating layers acrossthe second comb tooth portions 87C in the width direction are embeddedfrom the surface to the cavity 29C of the base substrate 9C.

The insulating layers 89C are made of SiO₂. The second comb toothportions 87C are insulated from other portions of the Z movableelectrode 82C by the insulating layers 89C.

On the surface of the base substrate 9C including the Z fixed electrode81C and the Z movable electrode 82C, as described above, a firstinsulating film 49C and a second insulating film 50C made of SiO₂ arelaminated in order.

Between the first insulating film 49C and the second insulating film50C, a Z first detection wiring 90C and a Z second detection wiring 91Care formed.

The Z first detection wiring 90C and the Z second detection wiring 91Care respectively connected to the first comb tooth portions 84C of the Zfixed electrode 81C and the second comb tooth portions 87C of the Zmovable electrode 82C adjacent to each other.

In detail, the Z first detection wiring 90C is formed along the firstbase portion 83C, and includes Al wirings branched toward the tip endportions of the first comb tooth portions 84C across the insulatinglayers 85C of the first comb tooth portions 84C.

The branched Al wirings are electrically connected to the tip end sidesrelative to the insulating layers 85C of the first comb tooth portions84C by penetrating through the first insulating film 49C.

As shown in FIG. 21, the Z first detection wiring 90C is led onto thesupport portion 32C via the first base portion 83C, and partiallyexposed as an electrode pad 15C.

The Z second detection wiring 91C is formed along the second baseportion 86C, and includes Al wirings branched toward the second combtooth portions 87C across the insulating layers 89C close to the baseend portions of the second comb tooth portions 87C.

The branched Al wirings are electrically connected to the second combtooth portions 87C by penetrating through the first insulating film 49C.

As shown in FIG. 21, the Z second detection wiring 91C is led onto thesupport portion 32C via the second base portion 86C, and partiallyexposed as an electrode pad 15C.

The upper surfaces and side surfaces of Z fixed electrode 81C and the Zmovable electrode 82C are coated by a protective thin film 54C made ofSiO₂ so that the first insulating film 49C and the second insulatingfilm 50C are covered.

In the Z-axis sensor 14C structured as described above, the first combtooth portions 84C (Z fixed electrode 81C) to which the Z firstdetection wiring 90C is connected and the second comb tooth portions 87C(Z movable electrode 82C) to which the Z second detection wiring 91C isconnected are opposed at an electrode-to-electrode distance d_(z) toconstitute a capacitor.

When acceleration in the Z-axis direction is applied to the Z movableelectrode 82C, the comb-tooth-like Z movable electrode 82C oscillates upand down like a pendulum similarly around the comb-tooth-like Z fixedelectrode 81C as a center of oscillation along the Z-axis direction withrespect to the Z fixed electrode 81C.

Accordingly, the opposing area S between the first comb tooth portions84C of the Z fixed electrode 81C and the second comb tooth portions 87Cof the Z movable electrode 82C adjacent to each other changes. Then, bydetecting a change in capacitance between the Z movable electrode 82Cand the Z fixed electrode 81C caused by the change in opposing area S,the acceleration a_(z) in the Z-axis direction is detected.

In the present preferred embodiment, the acceleration a_(z) in theZ-axis direction is obtained by calculating a difference between adetection value of the Z-axis sensor 14C surrounding the X-axis sensor12C and a detection value of the Z-axis sensor 14C surrounding theY-axis sensor 13C.

For example, as shown in FIG. 21, the difference can be obtained bymaking the position relationship between the fixed electrode and themovable electrode of the Z-axis sensor 14C surrounding the X-axis sensor12C opposite to the position relationship between the fixed electrodeand the movable electrode of the Z-axis sensor 14C surrounding theY-axis sensor 13C. Accordingly, the manner of oscillation of the Zmovable electrode 82C differs between the pair of Z-axis sensors 14C, sothat the difference occurs.

<Method for Manufacturing Acceleration Sensor>

Next, the manufacturing process of the above-described accelerationsensor will be described with reference to FIG. 26A to FIG. 26M in orderof steps. In this paragraph, only the manufacturing process of theZ-axis sensors is shown in the drawings, and the description of themanufacturing processes of the X-axis sensor and the Y-axis sensor areomitted, however, the manufacturing processes of the X-axis sensor andthe Y-axis sensor are performed in the same manner as the manufacturingprocess of the Z-axis sensors in parallel to the manufacturing processof the Z-axis sensors.

FIG. 26A to FIG. 26M are schematic sectional views showing parts of themanufacturing process of the Z-axis sensors shown in FIG. 21 in order ofsteps, illustrating a cutting plane taken at the same position as inFIG. 25.

To manufacture the Z-axis sensors 14C, as shown in FIG. 26A, the surfaceof the base substrate 9C made of conductive silicon is thermallyoxidized (for example, temperature: 1100 to 1200° C., film thickness:5000 Å). Accordingly, the first insulating film 49C is formed on thesurface of the base substrate 9C.

Next, by a known patterning technique, the first insulating film 49C ispatterned, and openings are formed in regions in which the insulatinglayers 85C and 89C should be embedded. Next, by anisotropic deep RIE(Reactive Ion Etching) using the first insulating film 49C as a hardmask, specifically, by a Bosch process, the base substrate 9C is dug.Accordingly, trenches 36C are formed in the base substrate 9C.

In the Bosch process, a step of etching the base substrate 9C by usingSF₆ (sulfur hexafluoride) and a step of forming a protective film on theetched surfaces by using C₄F₈ (perfluorocyclobutane) are alternatelyrepeated. Accordingly, the base substrate 9C can be etched at a highaspect ratio, however, a wavy irregularity called scallop is formed onthe etched surfaces (inner peripheral surfaces of the trenches).

Next, as shown in FIG. 26B, the insides of the trenches 36C formed inthe base substrate 9C and the surface of the base substrate 9C arethermally oxidized (for example, temperature: 1100 to 1200° C.), andthen, the surface of the oxide film is etched back (for example, thefilm thickness after etching back of the first insulating film 49C is21800 Å). Accordingly, the insulating layers 85C and 89C filling thetrenches are formed concurrently (only the insulating layer 89C isshown).

Next, as shown in FIG. 26C, the first insulating film 49C is etched.Accordingly, contact holes are formed in the first insulating film 49C.Next, contact plugs filling the contact holes are formed, and then, bysputtering, aluminum is deposited (for example, 7000 Å) on the firstinsulating film 49C, and this aluminum deposit layer is patterned.Accordingly, on the first insulating film 49C, the Z first detectionwiring 90C and the Z second detection wiring 91C are formed. At thistime, the electrode pads 15C are also formed on the first insulatingfilm 49C concurrently although this is not shown.

Next, as shown in FIG. 26D, by a CVD method, the second insulating film50C is laminated on the first insulating film 49C. Next, the secondinsulating film 50C and the first insulating film 49C on regions inwhich the cavity 29C of the base substrate 9C should be formed areremoved in order by etching. By etching the second insulating film 50C,openings for exposing the electrode pads 15C are formed in the secondinsulating film 50C although this is not shown.

Subsequently, a resist having openings in regions other than the regionsin which the Z fixed electrode 81C and the Z movable electrode 82Cshould be formed is formed on the second insulating film 50C.Subsequently, by anisotropic deep RIE using the resist as a mask,specifically, by a Bosch process, the base substrate 9C is dug.Accordingly, the surface portion of the base substrate 9C is molded intothe shapes of the Z fixed electrode 81C and the Z movable electrode 82C,and between these, the trenches 37C are formed.

Next, as shown in FIG. 26E, by thermal oxidization or by a PECVD method,on the entire surfaces of the Z fixed electrode 81C and the Z movableelectrode 82C and the entire inner surfaces of the trenches 37C (thatis, the side surfaces and the bottom surfaces defining the trenches37C), a protective thin film 54C made of SiO₂ is formed.

Next, as shown in FIG. 26F, the portions on the bottom surfaces of thetrenches 37C of the protective thin film 54C are removed by etchingback. Accordingly, the bottom surfaces of the trenches 37C are exposed.

Next, as shown in FIG. 26G, by anisotropic deep RIE using the remainingprotective thin film 54C as a mask, the bottom surfaces of the trenches37C are further dug. Accordingly, at the bottom portions of the trenches37C, exposure spaces 38C as recesses to which the crystal face of thebase substrate 9C is exposed are formed.

Next, as shown in FIG. 26H, by a PECVD method, SiN as a second inorganicmaterial is deposited on the entire surface of the base substrate 9C(the entire region including the sensor region 10C and the pad region11C) from above. Accordingly, a first sacrifice layer 39C (for example,thickness: 1 μm to 5 μm) that fills the upper portions of the exposurespaces 38C and covers the entire region including the sensor region 10Cand the pad region 11C is formed. Accordingly, the opening ends of theexposure spaces 38C are closed by the first sacrifice layer 39C and thelower portions of the exposure spaces 38C are kept hollow.

Next, as shown in FIG. 26I, by sputtering, Al as a metal material isdeposited on the entire surface of the first sacrifice layer 39C (theentire region including the sensor region 10C and the pad region 11C)from above the base substrate 9C. Accordingly, a second sacrifice layer40C (for example, thickness: 1 μm to 5 μm) thicker than the firstsacrifice layer 39C is formed on the first sacrifice layer 39C.

Subsequently, by a known patterning technique, the portions above thepad region 11C (not shown) in the second sacrifice layer 40C and thefirst sacrifice layer 39C are removed in order.

Next, as shown in FIG. 26J, by a PECVD method, SiO₂ as a first inorganicmaterial is deposited on the entire region of the base substrate 9C (theentire region including the sensor region 10C and the pad region 11C)from above. Accordingly, a protective layer 16C that adheres to the padregion 11C exposed from the first sacrifice layer 39C and the secondsacrifice layer 40C (specifically, the protective thin film 54C formedon the base substrate 9C) and covers the second sacrifice layer 40C isformed.

Next, as shown in FIG. 26K, by a known patterning technique, a largenumber of through holes 21C are formed in the top portion 18C of theprotective layer 16C.

Next, as shown in FIG. 26L, a fluorine-based gas (for example, NF₃, SF₆,XeF₂, etc.) as an etching medium is supplied to the second sacrificelayer 40C via the through holes 21C. Accordingly, the second sacrificelayer 40C is removed by etching. Accordingly, a space 17C is formeddirectly below the protective layer 16C.

Next, as shown in FIG. 26M, a chlorine-based gas (for example, Cl₂, HCl,BCl₃, etc.) as an etching medium is supplied to the first sacrificelayer 39C via the through holes 21C. Accordingly, the first sacrificelayer 39C is removed by etching. Accordingly, the opening ends of theexposure spaces 38C closed by the first sacrifice layer 39C, are opened.

Thereafter, via the through holes 21C, reactive ions and an etching gasare supplied into the exposure spaces 38C of the trenches 37C. Then, byaction of the reactive ions, etc., the base substrate 9C is etched in adirection parallel to the surface of the base substrate 9C while beingetched in the thickness direction of the base substrate 9C from theexposure spaces 38C. Accordingly, all exposure spaces 38C adjacent toeach other are integrated together to form a cavity 29C inside the basesubstrate 9C, and inside the cavity 29C, the Z fixed electrode 81C andthe Z movable electrode 82C float.

Through these steps, the Z-axis sensor 14C shown in FIG. 19 is obtained.

According to the above-described method, by forming the protective layer16C made of SiO₂ on the base substrate 9C in which the Z fixed electrode81C and the Z movable electrode 82C are formed, a layer that protectsthe sensor region 10C can be formed without using a bonding materialsuch as glass frit. Therefore, the cost for forming the protective layer16C can be reduced.

Concerning operability of formation of the protective layer 16C, theprotective layer 16C can be formed more easily than in the case where alid substrate is bonded by using a bonding material.

In detail, according to the present preferred embodiment, the firstsacrifice layer 39C made of SiN is formed by a PECVD method to cover thesensor region 10C in which the Z fixed electrode 81C and the Z movableelectrode 82C are formed (the step of FIG. 26H), and the secondsacrifice layer 40C made of Al is formed by sputtering to cover thefirst sacrifice layer 39C (the step of FIG. 26I). Then, by a knownpatterning technique (photolithography), these sacrifice layers 39C and40C are patterned. Next, a protective layer 16C made of SiO₂ is formedby a PECVD method to cover the patterned sacrifice layers 39C and 40C.Thereafter, by a known patterning technique, the through holes 21C areformed in the top portion 18C of the protective layer 16C, and bysupplying a fluorine-based etching gas and a chlorine-based etching gasin order via the through holes 21C, the second sacrifice layer 40C andthe first sacrifice layer 39C directly below the protective layer 16Care removed in order. Accordingly, the space 17C is formed at theportion at which the second sacrifice layer 40C existed, and theprotective layer 16C that covers the Z fixed electrode 81C and the Zmovable electrode 82C via the space 17C with respect to the sensorregion 10C is formed.

Therefore, without operations of position alignment of wafers, etc., bycombining known semiconductor device manufacturing techniques (a PECVDmethod, sputtering, photolithography, and etching), the protective layer16C can be easily formed.

In addition, when forming the sacrifice layers 39C and 40C for formingthe space 17C between the sensor region 10C and the protective layer16C, the cavity 29C is not formed directly below the Z fixed electrode81C and the Z movable electrode 82C, and these lower portions of theelectrodes 81C and 82C are fixed integrally to the base substrate 9C.Therefore, even if the sacrifice layers 39C and 40C come into contactwith the Z fixed electrode 81C and the Z movable electrode 82C, theelectrodes 81C and 82C are not oscillated by the impact of this contact.Therefore, it is not necessary to add a step, etc., for protecting theelectrodes 81C and 82C from the sacrifice layers 39C and 40C, so thatthe process can be prevented from becoming complicated.

In the present preferred embodiment, the space 17C is formed between theprotective layer 16C and the sensor region 10C by etching the secondsacrifice layer 40C made of Al. Specifically, what (second sacrificelayer 40C) is to be removed by etching is made of Al, and what(protective layer 16C) is to be left even after etching is made of SiO₂.Accordingly, when forming the space 17C, the etching selectivity of theprotective layer 16C to the second sacrifice layer 40C can be increased.

Therefore, even if the protective layer 16C is exposed to afluorine-based etching gas to be used for removing the second sacrificelayer 40C for a long period of time, the fluorine-based etching gas isfor etching Al, and therefore, erosion of the protective layer 16C madeof SiO₂ can be reduced. Therefore, the shape of the protective layer 16Ccan be excellently maintained.

On the other hand, in the case where the second sacrifice layer 40C madeof Al is used as a sacrifice layer that closes the opening ends of theexposure spaces 38C, if the second sacrifice layer 40C remains on the Zfixed electrode 81C and/or the Z movable electrode 82C, this secondsacrifice layer 40C may cause an operation failure of the sensor. Forexample, if the second sacrifice layer 40C remains across the Z fixedelectrode 81C and the Z movable electrode 82C, a short-circuit occursbetween the Z fixed electrode 81C and the Z movable electrode 82C viathis second sacrifice layer 40C.

Therefore, in the present preferred embodiment, as the sacrifice layerthat closes the opening ends of the exposure spaces 38C, the firstsacrifice layer 39C made of SiN is used. Accordingly, while the etchingselectivity of the protective layer 16C to the first sacrifice layer 39Cis secured, operation failures of the sensor can be prevented fromoccurring due to the sacrifice layer remaining.

According to the present preferred embodiment, on the entire surfaces ofthe Z fixed electrode 81C and the Z movable electrode 82C and the entireinner surfaces of the trenches 37C, the protective thin film 54C made ofSiO₂ having etching selectivity to the sacrifice layers 39C and 40C isformed. Therefore, when the sacrifice layers 39C and 40C are removed byetching, even if the etching gas comes into contact with the side wallsof the Z fixed electrode 81C and the Z movable electrode 82C, erosion(damage) of the Z fixed electrode 81C and the Z movable electrode 82Ccan be reduced. As a result, the variation in size (thicknesses T₁ andT₂ and the widths W₁ and W₂) of the Z fixed electrode 81C and the Zmovable electrode 82C can be reduced.

In the acceleration sensor 3C obtained by the above-described method,the Z fixed electrode 81C and the Z movable electrode 82C are covered bythe top portion 18C of the protective layer 16C. Accordingly, dust,etc., can be prevented from entering the inside of the protective layer16C from the outside of the protective layer 16C (from the side oppositeto the sensor region 10C with respect to the protective layer 16C).Therefore, the Z fixed electrode 81C and the Z movable electrode 82C canbe excellently protected from dust, etc. As a result, operation failuresof the sensor can be reduced.

In addition, the base substrate 9C is a conductive silicon substrate, sothat even without applying a special treatment for giving conductivityto the Z fixed electrode 81C and the Z movable electrode 82C molded intopredetermined shapes, the molded structures can be used as they are aselectrodes. Portions except for the portions to be used as electrodescan be used as wirings (Z first detection wiring 90C and Z seconddetection wiring 91C).

The operation and effects in the Z-axis sensors 14C are described indetail above, and the same operation and effects (reduction in cost dueto the protective layer 16C, simplification of the manufacturingprocess, shape maintenance of the protective layer 16C, prevention ofoperation failures of the sensor, and stabilization of the sizes of theelectrodes, etc.) as in the Z-axis sensors 14C can also be obtained inthe X-axis sensor 12C and the Y-axis sensor 13C.

The MEMS package 1C according to the present preferred embodimentincludes the X-axis sensor 12C, the Y-axis sensor 13C, and the Z-axissensors 14C, so that operation failures of the sensor can be reduced. Asa result, a highly reliable MEMS package can be provided.

The third preferred embodiment of the present invention is describedabove, however the present invention can also be carried out in otherembodiments.

For example, the MEMS package 1C may include an angular velocity sensorinstead of or in addition to the acceleration sensor 3C. This angularvelocity sensor can be manufactured by providing circuits for driving,for example, the movable electrodes 42C, 62C, and 82C in the sensors 12Cto 14C shown in FIG. 21 to FIG. 25.

For example, a Z-axis angular velocity sensor 92C that detects anangular velocity ω_(x) applied around the X axis includes, as shown inFIG. 27, insulating layers 94C embedded in both sides of the portion(opposed portion 93C) opposed to the tip end portion 95C (describedlater) of each second comb tooth portion 87C on the first base portion83C in the Z-axis sensor 14C shown in FIG. 24. The opposed portion 93Csurrounded by the insulating layers 94C and the triangular space of thetruss structure is insulated from other portions of the first baseportion 83C.

Further, the Z-axis angular velocity sensor 92C includes insulatinglayers 98C embedded in portions close to the tip end portions 95C of thesecond comb tooth portions 87C. Each second comb tooth portion 87C ispartitioned into the tip end portion 95C, the intermediate portion 96C,and the base end portion 97C by the insulating layers 89C and 98C.

Further, the Z-axis angular velocity sensor 92C includes Z first drivewiring 99C and Z second drive wiring 100C connected to the opposedportions 93C of the first base portion 83C and the tip end portions 95Cof the second comb tooth portions 87C, respectively.

In this Z-axis angular velocity sensor 92C, the opposed portions 93C ofthe Z fixed electrode 81C and the tip end portions 95C of the Z movableelectrode 82C opposed to each other at an interval therebetweenconstitute drive portions between which drive voltages are applied tooscillate the Z movable electrode 82C by coulomb forces generated bychanges in the drive voltages.

Between the opposed portions 93C of the Z fixed electrode 81C and thetip end portions 95C of the Z movable electrode 82C, drive voltages withthe same polarity and drive voltages with different polarities arealternately applied via the Z first drive wiring 99C and the Z seconddrive wiring 100C. Accordingly, coulomb repulsive and attractive forcesare alternately generated between the opposed portions 93C and the tipend portions 95C.

As a result, the comb-tooth-like Z movable electrode 82C oscillates upand down like a pendulum similarly around the comb-tooth-like Z fixedelectrode 81C as a center of oscillation along the Z-axis direction withrespect to the Z fixed electrode 81C (oscillation Uz).

In this state, when the Z movable electrode 82C rotates around the Xaxis as a central axis, a coriolis force F_(y) is generated in theY-axis direction. This coriolis force F_(y) changes the opposing areaand/or electrode-to-electrode distance d_(z) between the first combtooth portions 84C and the intermediate portions 96C of the second combtooth portions 87C adjacent to each other.

Then, by detecting a change in capacitance between the Z movableelectrode 82C and the Z fixed electrode 81C caused by the change inopposing area and/or electrode-to-electrode distance d_(z), the angularvelocity ω_(x) around the X axis is detected.

The material of the protective layer 16C is not limited to SiO₂ as longas the material is an inorganic material, and may be, for example, SiN.In this case, in order to secure the etching selectivity of the firstsacrifice layer 39C to the protective layer 16C, the first sacrificelayer 39C is preferably made of SiO₂.

In the preferred embodiment described above, a sacrifice layer having atwo-layer structure including the first sacrifice layer 39C and thesecond sacrifice layer 40C is formed, however, the sacrifice layer mayhave a single-layer structure, a three-layer structure, a four-layerstructure, and five or more-layer structures as long as the material ofthe sacrifice layer has etching selectivity to the protective layer 16Cand the base substrate 9C.

(4) Fourth Preferred Embodiment <Entire Arrangement of MEMS Package>

FIG. 28 is a schematic perspective view of a MEMS package according to afourth preferred embodiment of the present invention.

The MEMS package 1D is used for, for example, correction of shake of avideo camera or a still camera, position detection of a car navigationsystem, and motion detection of a robot and a gaming machine, etc.

The MEMS package 1D includes a substrate 2D, an angular velocity sensor3D as a MEMS sensor, external terminals 4D, an integrated circuit 5D(ASIC: Application Specific Integrated Circuit), and a resin package 6D.

The substrate 2D is formed to have a rectangular plate shape having asurface and a back surface.

The angular velocity sensor 3D is disposed on one end portion in thelongitudinal direction on the surface side of the substrate 2D. Theangular velocity sensor 3D includes a base substrate 7D having a squareplate shape formed of a Si substrate, a sensor portion 8D provided atthe central portion of the base substrate 7D, and electrode pads 9D thatare disposed on the lateral side of the sensor portion 8D on the basesubstrate 7D to supply a voltage to the sensor portion 8D.

The sensor portion 8D includes an X-axis sensor 10D, a Y-axis sensor11D, and Z-axis sensors 12D as sensors that respectively detect angularvelocities around three axes orthogonal to each other in athree-dimensional space. These three sensors 10D to 12D are covered andsealed by a lid substrate 13D that is formed of, for example, a Sisubstrate and bonded to the base substrate 7D.

The X-axis sensor 10D generates a coriolis force Fz in the Z-axisdirection by using oscillation Ux in the X-axis direction when the MEMSpackage 1D is tilted, and detects an angular velocity ωy applied aroundthe Y axis by detecting a change in capacitance caused by the coriolisforce. The Y-axis sensor 11D generates a coriolis force Fx in the X-axisdirection by using oscillation Uy in the Y-axis direction when the MEMSpackage 1D is tilted, and detects an angular velocity ωz applied aroundthe Z axis by detecting a change in capacitance caused by the coriolisforce. The Z-axis sensor 12D generates a coriolis force Fy in the Y-axisdirection by using oscillation Uz in the Z-axis direction when the MEMSpackage 1D is tilted, and detects an angular velocity ωx applied aroundthe X axis by detecting a change in capacitance caused by the coriolisforce.

A plurality (seven in FIG. 28) of the electrode pads 9D are provided ateven intervals along the width direction orthogonal to the longitudinaldirection of the substrate 2D.

A plurality (twelve in FIG. 28) of the external terminals 4D areprovided at even intervals along the width direction of the substrate 2Don the other end portion in the longitudinal direction of the substrate2D (end portion on the side opposite to the angular velocity sensor 3D).The external terminals 4D are formed to penetrate through the substrate2D in the thickness direction, and are exposed as internal pads 14D tothe surface of the substrate 2D and exposed as external pads 15D to theback surface of the substrate 2D.

The integrated circuit 5D is disposed between the angular velocitysensor 3D and the external terminals 4D (internal pads 14D) on thesurface side of the substrate 2D. The integrated circuit 5D is formedof, for example, a Si substrate having a rectangular plate shape long inthe width direction of the substrate 2D. Inside this Si substrate,charge amplifiers that amplify electric signals output from the sensors10D to 12D, filter circuits (low-pass filters: LPF, etc.) that extractspecific frequency components of the electric signals, and logiccircuits that carry out logic operations of filtered electric signals,etc., are formed. These circuits consist of, for example, CMOS devices.The integrated circuit 5D includes first electrode pads 16D and secondelectrode pads 17D.

A plurality (seven in FIG. 28) of first electrode pads 16D are providedat even intervals along the width direction of the substrate 2D at anend portion on the side close to the angular velocity sensor 3D in thelongitudinal direction of the substrate 2D. The first electrode pads 16Dare connected one-to-one to the electrode pads 9D of the angularvelocity sensor 3D by bonding wires 18D.

A plurality (twelve in FIG. 28) of the second electrode pads 17D areprovided at even intervals along the width direction of the substrate 2Don an end portion on the side close to the external terminals 4D in thelongitudinal direction of the substrate 2D. The second electrode pads17D are connected one-to-one to the internal pads 14D of the externalterminals 4D by bonding wires 19D.

The resin package 6D defines the external shape of the MEMS package 1Din cooperation with the substrate 2D, and is formed to have asubstantially rectangular parallelepiped shape. The resin package 6D ismade of, for example, a known molding resin such as epoxy resin, andcovers the bonding wires 18D and 19D and the internal pads 14D as wellas the angular velocity sensor 3D and the integrated circuit 5D, andseals the angular velocity sensor 3D and the integrated circuit 5D insuch a manner that the external pads 15D are exposed.

<Arrangement of Z-Axis Sensors>

Next, an arrangement of the Z-axis sensors 12D will be described withreference to FIG. 29.

The angular velocity sensor 3D includes a base substrate 7D (forexample, thickness: 625 μm) as described above.

On the surface 20D of the base substrate 7D, abase insulating film 21D(for example, thickness: 10000 Å) is formed. The base insulating film21D is made of SiO₂ (silicon oxide).

On the base insulating film 21D, a drive electrode 22D (for example,thickness: 5000 Å) is formed as a lower electrode. The drive electrode22D is made of polysilicon.

Further, on the base insulating film 21D, an electrode coating film 23D(for example, thickness: 5000 Å) that coats the drive electrode 22D isformed. The electrode coating film 23D is made of SiO₂. In the electrodecoating film 23D, an opening 25D for exposing a portion of the driveelectrode 22D as a pad 24D is formed.

On the electrode coating film 23D, a polysilicon layer 26D (for example,thickness: 10 μm) is formed. The polysilicon layer 26D includes a fixedelectrode 27D and a movable electrode 28D as an upper electrode and acontact electrode 29D.

The fixed electrode 27D includes a contact portion 31D provided to standon the surface 30D of the electrode coating film 23D, and comb toothportions 32D formed of a plurality of electrodes aligned like comb teethalong the surface 20D of the base substrate 7D above the electrodecoating film 23D.

The contact portion 31D of the fixed electrode 27D includes a baseportion 33D (for example, height: 5 μm) fixed to the surface 30D of theelectrode coating film 23D, and a joint portion 34D that is joinedintegrally to the top portion of the base portion 33D and has the samethickness (described later) as the comb tooth portions 32D.

The joint portion 34D is formed to bulge more to the outside than theside surfaces 35D of the base portion 33D. Accordingly, between the sidesurfaces 36D of the joint portion 34D and the side surfaces 35D of thebase portion 33D, a step S₁ is formed.

The comb tooth portions 32D of the fixed electrode 27D are formedintegrally with the joint portion 34D of the contact portion 31D, andone end of the comb tooth portions 32D is supported by the joint portion34D so that a cavity 37D is formed between the comb tooth portions 32Dand the surface 30D of the electrode coating film 23D. Specifically, thecomb tooth portions 32D are supported in a floating state by the heightof the base portion 33D of the contact portion 31D from the surface 30Dof the electrode coating film 23D. The thickness of the comb toothportions 32D (the height from the top portion of the base portion 33D tothe surface of the polysilicon layer 26D) is, for example, approximately15 μm.

The movable electrode 28D includes a contact portion 38D provided tostand on the surface 30D of the electrode coating film 23D and combtooth portions 39D that consist of a plurality of electrodes disposed onthe respective portions between the comb tooth portions 32D of the fixedelectrode 27D above the electrode coating film 23D, and engage with thecomb tooth portions 32D of the fixed electrode 27D as a whole. Adistance (electrode-to-electrode distance d₁) of, for example,approximately 2 μm is provided between the comb tooth portions 39D andthe comb tooth portions 32D of the fixed electrode 27D.

The contact portion 38D of the movable electrode 28D is provided on theside opposite to the comb tooth portions 32D of the fixed electrode 27Dwith respect to the contact portion 31D of the fixed electrode 27D. Thecontact portion 38D includes a base portion 40D (for example, height: 5μm) fixed to the surface 30D of the electrode coating film 23D, and ajoint portion 41D joined integrally to the top portion of the baseportion 40D and having the same thickness (described later) as that ofthe comb tooth portions 39D.

The joint portion 41D is formed to bulge more to the outside than theside surfaces 42D of the base portion 40D. Accordingly, a step S₂ isformed between the side surfaces 43D of the joint portion 41D and theside surfaces 42D of the base portion 40D.

The comb tooth portions 39D of the movable electrode 28D are formedintegrally with the joint portion 41D of the contact portion 38D, andone end of the comb tooth portions 39D is supported by the joint portion41D so that a cavity 37D is formed between the comb tooth portions 39Dand the surface 30D of the electrode coating film 23D in the same manneras the comb tooth portions 32D of the fixed electrode 27D. Specifically,the comb tooth portions 39D are supported in a floating state by theheight of the base portion 40D of the contact portion 38D from thesurface 30D of the electrode coating film 23D. The thickness of the combtooth portions 39D (the height from the top portion of the base portion40D to the surface of the polysilicon layer 26D) is, for example,approximately 15 μm.

In the present preferred embodiment, directly below the cavity 37D, thedrive electrode 22D is formed across the comb teeth on both ends (inFIG. 29, the comb tooth portion 32D closest to the contact electrode 29Dand the comb tooth portion 39D closest to the contact portion 31D of thefixed electrode 27D) so as to extend across the comb tooth portions 32Dand 39D of the fixed electrode 27D and the movable electrode 28D thatengage with each other like comb teeth. Accordingly, one drive electrode22D is opposed to all the comb tooth portions 32D and 39D of the fixedelectrode 27D and the movable electrode 28D.

The contact electrode 29D includes a base portion 44D (for example,height: 5 μm) connected to the drive electrode 22D via the opening 25Dof the electrode coating film 23D and a joint portion 45D joinedintegrally to the top portion of the base portion 44D.

The joint portion 45D is formed to bulge more to the outside than theside surfaces 46D of the base portion 44D. Accordingly, between the sidesurfaces 47D of the joint portion 45D and the side surfaces 46D of thebase portion 44D, a step S₃ is formed.

On the polysilicon layer 26D, a surface protective film 48D (forexample, thickness: 3000 Å) made of SiO₂ is formed. Accordingly, thesurfaces of the comb tooth portions 32D and 39D and the contact portions31D and 38D (joint portions 34D and 41D) of the fixed electrode 27D andthe movable electrode 28D and the contact electrode 29D are covered bythe surface protective film 48D.

On the surface protective film 48D, at portions opposed to the contactportion 31D of the fixed electrode 27D, the contact portion 38D of themovable electrode 28D, and the contact electrode 29D, a first detectionwiring 49D, a second detection wiring 50D, and a drive wiring 51D areformed, respectively. The wirings 49D to 51D are made of Al (aluminum),and are connected to the contact portion 31D of the fixed electrode 27D,the contact portion 38D of the movable electrode 28D, and the contactelectrode 29D, respectively, by penetrating through the surfaceprotective film 48D.

In the Z-axis sensor 12D structured as described above, drive voltageswith the same polarity and drive voltages with different polarities arealternately applied between the comb tooth portions 39D of the movableelectrode 28D and the drive electrode 22D. Accordingly, coulombrepulsive and attractive forces are alternately generated between thecomb tooth portions 39D of the movable electrode 28D and the driveelectrode 22D.

As a result, the comb-tooth-like movable electrode 28D oscillates up anddown like a pendulum similarly around the comb-tooth-like fixedelectrode 27D as a center of oscillation along the Z-axis direction withrespect to the fixed electrode 27D (oscillation Uz).

In this state, when the movable electrode 28D rotates around the X axisas a central axis, a coriolis force Fy is generated in the Y-axisdirection. This coriolis force Fy changes the opposing area and/orelectrode-to-electrode distance d₁ between the comb tooth portions 39Dof the movable electrode 28D and the comb tooth portions 32D of thefixed electrode 27D adjacent to each other.

Then, by detecting a change in capacitance C between the movableelectrode 28D and the fixed electrode 27D caused by the change inopposing area and/or electrode-to-electrode distance d₁, the angularvelocity ωx around the X axis is detected.

<Method for Manufacturing Angular Velocity Sensor>

Next, with reference to FIG. 30A to FIG. 30L, the manufacturing processof the above-described angular velocity sensor will be described inorder of steps. In this paragraph, only the manufacturing process of theZ-axis sensors is shown in the drawings, and the description of themanufacturing processes of the X-axis sensor and the Y-axis sensor areomitted, however, the manufacturing processes of the X-axis sensor andthe Y-axis sensor are performed in parallel to the manufacturing processof the Z-axis sensors in the same manner as the manufacturing process ofthe Z-axis sensors.

FIG. 30A to FIG. 30L are sectional views showing parts of themanufacturing process of the Z-axis sensors shown in FIG. 29,illustrating a section taken at the same position as in FIG. 29.

To manufacture the Z-axis sensor 12D, as shown in FIG. 30A, the surface20D of the base substrate 7D made of conductive silicon is thermallyoxidized (for example, temperature: 1000° C. to 1200° C.). Accordingly,on the surface 20D of the base substrate 7D, a base insulating film 21Dmade of SiO₂ is formed. Next, by a CVD (Chemical Vapor Deposition)method, polysilicon is deposited on the entire surface of the baseinsulating film 21D. Subsequently, by a known patterning technique, thepolysilicon is selectively patterned to form the drive electrode 22D.

Next, as shown in FIG. 30B, by a CVD method, the electrode coating film23D made of SiO₂ having etching selectivity to polysilicon is formed onthe entire surface of the base insulating film 21D. Accordingly, thedrive electrode 22D is completely coated by the electrode coating film23D.

Here, the material having etching selectivity to polysilicon (in thisparagraph, defined as material A) is, for example, a material satisfyinga ratio (etching selectivity) of the etching rate of polysilicon to acertain etching medium to the etching rate of material A to the etchingmedium=(etching rate of material A/etching rate of polysilicon)≠1. Inparticular, the material A preferably makes the etching selectivitycloser to 0 (zero) (etching selectivity≈0), and in detail, the materialA is preferably SiO₂ as in the present preferred embodiment. Theelectrode coating film 23D may be made of other materials (for example,SiN, etc.) having etching selectivity to polysilicon.

Next, as shown in FIG. 30C, by a CVD method, polysilicon (for example,thickness: 5000 Å) is deposited on the entire region of the surface 30Dof the electrode coating film 23D. Subsequently, by a known patterningtechnique, the polysilicon is selectively patterned to form a sacrificepolysilicon layer 52D.

Next, as shown in FIG. 30D, by a CVD method, a sacrifice oxide film 53Dmade of SiO₂ (for example, thickness: 5000 Å) is formed on the entiresurface of the sacrifice polysilicon layer 52D.

Next, as shown in FIG. 30E, by a known patterning technique, thesacrifice oxide film 53D is patterned, and the portions at which thebase portions 33D, 40D, and 44D should be formed of the sacrifice oxidefilm 53D are selectively removed, and accordingly, openings 25D, 54D,and 55D are formed. Accordingly, a portion of the drive electrode 22D isexposed as a pad 24D from the opening 25D.

Next, on the sacrifice oxide film 53D, a seed film made of polysiliconis formed. Subsequently, from this seed film, polysilicon is epitaxiallygrown. Accordingly, as shown in FIG. 30F, a polysilicon layer 26D (forexample, thickness: 15 μm) is formed as an electrode polysilicon layer.

Next, as shown in FIG. 30G, CMP (Chemical Mechanical Polishing) isapplied until the surface of the polysilicon layer 26D becomes flush.Accordingly, the thickness of the polysilicon layer 26D changes from,for example, 15 μm to 10 μm. Subsequently, by a CVD method, a surfaceprotective film 48D made of SiO₂ is formed on the entire surface of thepolysilicon layer 26D. Subsequently, by a known patterning technique,the surface protective film 48D is selectively removed. Accordingly,contact holes are formed in the surface protective film 48D.Subsequently, after contact plugs filling the contact holes are formed,Al is deposited by sputtering on the surface protective film 48D, andthis Al deposition layer is patterned. Accordingly, wirings 49D to 51Dare formed concurrently on the surface protective film 48D.

Next, as shown in FIG. 30H, by a known patterning technique, openingsare formed in regions except for the regions in which the fixedelectrode 27D, the movable electrode 28D, and the contact electrode 29Dshould be formed in the surface protective film 48D. Subsequently, byanisotropic deep RIE using the remaining surface protective film 48D asa hard mask, specifically, by a Bosch process, the polysilicon layer 26Dis dug. In the Bosch process, a step of etching the polysilicon layer26D by using SF₆ (sulfur hexafluoride) and a step of forming aprotective film on the etched surfaces by using C₄F₈(perfluorocyclobutane) are alternately repeated. Accordingly, thepolysilicon layer 26D can be etched at a high aspect ratio, however, awavy irregularity called scallop is formed on the etched surfaces (innerperipheral surfaces of the trenches).

Accordingly, the polysilicon layer 26D is molded into the shapes of thefixed electrode 27D, the movable electrode 28D, and the contactelectrode 29D, and between these portions (the comb tooth portions 32Dand 39D and the contact portions 31D and 38D, etc.), trenches 56D areformed. The surface of the sacrifice oxide film 53D is exposed to thebottom surfaces of the trenches 56D.

Next, as shown in FIG. 30I, by a CVD method, a protective thin film 57Dmade of SiO₂ is formed on the entire surfaces of the fixed electrode27D, the movable electrode 28D, and the contact electrode 29D and theentire inner surfaces of the trenches 56D (that is, the side surfacesand the bottom surfaces defining the trenches 56D).

Next, as shown in FIG. 30J, by anisotropic deep RIE, the bottom surfacesof the trenches 56D are further dug. Accordingly, the sacrificepolysilicon layer 52D is exposed as the bottom surfaces of the trenches56D.

Subsequent to this anisotropic deep RIE, reactive ions and etching gas(for example, SF₆ gas) are supplied into the trenches 56D by isotropicRIE. Then, by action of the reactive ions, etc., as shown in FIG. 30K,the sacrifice polysilicon layer 52D is etched in the direction parallelto the surface of the base substrate 7D while being etched in thethickness direction of the base substrate 7D from the bottom portions ofthe trenches 56D. Accordingly, the bottom portions of all trenches 56Dadjacent to each other are integrated together to form a cavity 37D, anddirectly above the cavity 37D, the fixed electrode 27D (comb toothportions 32D) and the movable electrode 28D (comb tooth portions 39D)are in a floating state.

Next, as shown in FIG. 30L, an etching gas (for example, HF(hydrofluoric acid) gas) is supplied into the trenches 56D. By theaction of this HF gas, the protective thin film 57D and the sacrificeoxide film 53D made of SiO₂ are removed.

Through the above-described steps, the Z-axis sensor 12D shown in FIG.29 is obtained.

According to the above-described method, after the drive electrode 22Dis formed on the base substrate 7D (the step of FIG. 30A), the fixedelectrode 27D and the movable electrode 28D for angular velocitydetection in the Z-axis sensor 12D are formed by using the polysiliconlayer 26D on the base substrate 7D. Therefore, before forming the fixedelectrode 27D and the movable electrode 28D, the drive electrode 22D canbe easily formed directly below the fixed electrode 27D and the movableelectrode 28D.

Further, in the manufacturing process of the Z-axis sensors 12D, betweenthe drive electrode 22D and the polysilicon layer 26D, the sacrificepolysilicon layer 52D and the sacrifice oxide film 53D are formed (thesteps of FIG. 30C and FIG. 30D). These sacrifice layers 52D and 53D areremoved after the polysilicon layer 26D is molded into the fixedelectrode 27D and the movable electrode 28D (the steps of FIG. 30K andFIG. 30L). Therefore, the cavity 37D can be easily formed between thefixed electrode 27D (comb tooth portions 32D), the movable electrode 28D(comb tooth portions 39D) and the drive electrode 22D. Accordingly, theZ-axis sensor 12D including a capacitor in which the fixed electrode 27D(comb tooth portions 32D), the movable electrode 28D (comb toothportions 39D) are opposed to the drive electrode 22D vertically via thecavity 37D can be manufactured.

Therefore, in the step of FIG. 30A, by adjusting the area of the driveelectrode 22D to an appropriate size, the capacitor capacity between themovable electrode 28D (comb tooth portions 39D) and the drive electrode22D can be controlled to an optimum capacity for sensor operation.

In detail, the drive electrode 22D is formed across comb teeth on bothends so as to extend across the comb tooth portions 32D and 39D of thefixed electrode 27D and the movable electrode 28D. Accordingly, the areaof the drive electrode 22D opposed to the movable electrode 28D (combtooth portions 39D) can be made larger than the opposing area of thefixed electrode 27D (comb tooth portions 32D) to the movable electrode28D (comb tooth portions 39D). Therefore, as compared with a case wheredrive voltages are applied between the fixed electrode 27D and themovable electrode 28D that engage with each other like comb teeth, themovable electrode 28D can be oscillated with a larger amplitude. As aresult, the angular velocity detection sensitivity can be improved.

In addition, even after the cavity 37D is formed by removing thesacrifice polysilicon layer 52D and the sacrifice oxide film 53D, thedrive electrode 22D is covered by the electrode coating film 23D.Therefore, even if the movable electrode 28D approaches the driveelectrode 22D due to great oscillation, the movable electrode 28D (combtooth portions 39D) and the drive electrode 22D can be prevented fromcoming into contact with each other. As a result, the movable electrode28D (comb tooth portions 39D) and the drive electrode 22D can beprevented from being short-circuited by each other. Therefore, operationfailures of the sensor can be reduced.

As a result, according to the MEMS package 1D, the detection accuracy ofthe Z-axis sensors 12D can be improved.

In the manufactured Z-axis sensor 12D, if the protective thin film 57Dremains on the side walls of the fixed electrode 27D and the movableelectrode 28D, as compared with the present preferred embodiment inwhich the protective thin film 57D is not provided, the fixed electrode27D and the movable electrode 28D are easily charged. Therefore, forexample, when a voltage X (V) is applied between the fixed electrode 27Dand the movable electrode 28D, the Z-axis sensor 12D may erroneouslyrecognize a potential difference between the fixed electrode 27D and themovable electrode 28D caused by charging as a voltage applied betweenthe fixed electrode 27D and the movable electrode 28D, that is, aso-called memory effect may occur. As a result, there is a possibilitythat a voltage lower than the voltage X (V) is applied between the fixedelectrode 27D and the movable electrode 28D and the designed detectionperformance cannot be realized.

Therefore, in the Z-axis sensor 12D of the present preferred embodiment,after the cavity 37D is formed, by removing the protective thin film 57D(the step of FIG. 30L), the side walls of the fixed electrode 27D andthe movable electrode 28D are exposed. Therefore, the occurrence of thememory effect described above can be reduced. As a result, a necessaryand sufficient voltage can be applied between the fixed electrode 27Dand the movable electrode 28D, so that the designed detectionperformance can be reliably realized.

In the Z-axis sensor 12D, by using a portion of the polysilicon layer26D forming the fixed electrode 27D and the movable electrode 28D, thecontact electrode 29D is formed in the same layer as that of the fixedelectrode 27D and the movable electrode 28D. Therefore, all contactswith the fixed electrode 27D, the movable electrode 28D, and the driveelectrode 22D can be collectively formed as the wirings 49D to 51Dformed on the same layer (polysilicon layer 26D). As a result, thesewirings 49D to 51D can be formed in the same step, so that the number ofmanufacturing steps can be reduced. Therefore, the cost can be reduced.

The fourth preferred embodiment of the present invention is describedabove, however the present invention can also be carried out in otherembodiments.

For example, the MEMS package 1D may include an acceleration sensorinstead of or in addition to the angular velocity sensor 3D. Theacceleration sensor can be manufactured, for example, by forming thecapacitor formed between the drive electrode 22D and the movableelectrode 28D as a capacitor for acceleration detection.

For example, as shown in FIG. 31, in a Z-axis acceleration sensor 60Dthat detects acceleration applied in the Z-axis direction, in additionto the capacitor consisting of the fixed electrode 27D (comb toothportions 32D) and the movable electrode 28D (comb tooth portions 39D), acapacitor consisting of the movable electrode 28D (comb tooth portions39D) and a second fixed electrode 61D opposed to each other via thecavity 37D and the electrode coating film 23D (at electrode-to-electrodedistance d₂) along the Z-axis direction can be used for sensoroperations. Accordingly, the capacitor relating to accelerationdetection operations of the sensor can be increased, so that theacceleration applied to the MEMS package 1D can be accurately detected.

In the above-described embodiment, in the step of FIG. 30L, theprotective thin film 57D and the sacrifice oxide film 53D are removed,however, the protective thin film 57D and the sacrifice oxide film 53Dmay be left by omitting the step of FIG. 30L as shown in FIG. 32.

(5) Fifth Preferred Embodiment <Entire Arrangement of MEMS Package>

FIG. 33 is a schematic perspective view of a MEMS package according to afifth preferred embodiment of the present invention.

The MEMS package 1E is used for, for example, correction of shake of avideo camera or a still camera, position detection of a car navigationsystem, and motion detection of a robot and a gaming machine, etc.

The MEMS package 1E includes a substrate 2E, an angular velocity sensor3E as a MEMS sensor, external terminals 4E, an integrated circuit 5E(ASIC: Application Specific Integrated Circuit), and a resin package 6E.

The substrate 2E is formed to have a rectangular plate shape having asurface and a back surface.

The angular velocity sensor 3E is disposed on one end portion in thelongitudinal direction on the surface side of the substrate 2E. Theangular velocity sensor 3E includes a base substrate 7E formed of a Sisubstrate having a square plate shape, a sensor portion 8E provided atthe central portion of the base substrate 7E, and electrode pads 9E thatare disposed on the lateral side of the sensor portion 8E on the basesubstrate 7E and supply a voltage to the sensor portion 8E.

The sensor portion 8E includes an X-axis sensor 10E, a Y-axis sensor11E, and Z-axis sensors 12E as sensors that respectively detect angularvelocities around three axes orthogonal to each other in athree-dimensional space. These three sensors 10E to 12E are covered andsealed by a lid substrate 13E formed of, for example, a Si substrate andbonded to the base substrate 7E.

The X-axis sensor 10E generates a coriolis force Fz in the Z-axisdirection by using oscillation Ux in the X-axis direction when the MEMSpackage 1E is tilted, and detects an angular velocity ωy applied aroundthe Y axis by detecting a change in capacitance caused by the coriolisforce. The Y-axis sensor 11E generates a coriolis force Fx in the X-axisdirection by using oscillation Uy in the Y-axis direction when the MEMSpackage 1E is tilted, and detects an angular velocity ωz applied aroundthe Z axis by detecting a change in capacitance caused by the coriolisforce. The Z-axis sensor 12E generates a coriolis force Fy in the Y-axisdirection by using oscillation Uz in the Z-axis direction when the MEMSpackage 1E is tilted, and detects an angular velocity ωx applied aroundthe X axis by detecting a change in capacitance caused by the coriolisforce.

A plurality (seven in FIG. 33) of the electrode pads 9E are provided ateven intervals along the width direction orthogonal to the longitudinaldirection of the substrate 2E.

A plurality (twelve in FIG. 33) of the external terminals 4E areprovided at even intervals along the width direction of the substrate 2Eon the other end portion in the longitudinal direction of the substrate2E (the end portion on the side opposite to the angular velocity sensor3E). The external terminals 4E are formed to penetrate through thesubstrate 2E in the thickness direction, and are exposed as internalpads 14E to the surface of the substrate 2E and exposed as external pads15E to the back surface of the substrate 2E.

The integrated circuit 5E is disposed between the angular velocitysensor 3E and the external terminals 4E (internal pads 14E) on thesurface side of the substrate 2E. The integrated circuit 5E is formedof, for example, a Si substrate having a rectangular plate shape long inthe width direction of the substrate 2E. Inside the Si substrate, chargeamplifiers that amplify electric signals output from the sensors 10E to12E, filter circuits (low-pass filters: LPF, etc.) that extract specificfrequency components of the electric signals, and logic circuits thatcarry out logic operations of filtered electric signals, etc., areformed. These circuits consist of, for example, CMOS devices. Theintegrated circuit 5E includes first electrode pads 16E and secondelectrode pads 17E.

A plurality (seven in FIG. 33) of the first electrode pads 16E areprovided at even intervals along the width direction of the substrate 2Eon the end portion on the side close to the angular velocity sensor 3Ein the longitudinal direction of the substrate 2E. The first electrodepads 16E are connected one-to-one to the electrode pads 9E of theangular velocity sensor 3E by bonding wires 18E.

A plurality (twelve in FIG. 33) of the second electrode pads 17E areprovided at even intervals along the width direction of the substrate 2Eon the end portion on the side close to the external terminals 4E in thelongitudinal direction of the substrate 2E. The second electrode pads17E are connected one-to-one to the internal pads 14E of the externalterminals 4E by bonding wires 19E.

The resin package 6E defines the external shape of the MEMS package 1Ein cooperation with the substrate 2E, and is formed to have asubstantially rectangular parallelepiped shape. The resin package 6E ismade of, for example, a known molding resin such as epoxy resin, andcovers the bonding wires 18E and 19E and the internal pads 14E togetherwith the angular velocity sensor 3E and the integrated circuit 5E, andseals the angular velocity sensor 3E and the integrated circuit 5E insuch a manner that the external pads 15E are exposed.

<Arrangement of X-Axis Sensor and Y-Axis Sensor>

Next, with reference to FIG. 34 to FIG. 36, an arrangement of the X-axissensor and the Y-axis sensor will be described.

FIG. 34 is a schematic plan view of the angular velocity sensor shown inFIG. 1. FIG. 35 is a plan view of a principal portion of the X-axissensor shown in FIG. 2. FIG. 36 is a sectional view of the principalportion of the X-axis sensor shown in FIG. 2, illustrating a sectiontaken along the cutting plane H-H in FIG. 35.

The angular velocity sensor 3E includes a base substrate 7E formed of aSi substrate as described above. On the surface layer portion of thebase substrate 7E (the portion opposed to the lid substrate 13E of thebase substrate 7E), a recess 20E having a rectangular shape in a planview is formed.

On the base substrate 7E, a base insulating layer 21E (for example,thickness: 2 μm to 10 μm) as a base film and a polysilicon layer 22E(for example, thickness: 5 μm to 20 μm) are laminated in order so as tocover the recess 20E. Accordingly, inside the lamination structureconsisting of the base substrate 7E, the base insulating layer 21E, andthe polysilicon layer 22E of the angular velocity sensor 3E, a cavity23E partitioned by the base insulating layer 21E and the base substrate7E is formed.

The X-axis sensor 10E, the Y-axis sensor 11E, and the Z-axis sensors 12Ehave a lamination structure including the base insulating layer 21E andthe polysilicon layer 22E, and are disposed directly above the cavity23E. Specifically, the X-axis sensor 10E, the Y-axis sensor 11E, and theZ-axis sensors 12E are provided in a floating state with respect to thebottom wall 24E of the base substrate 7E forming the bottom surface thatpartitions the cavity 23E from the back surface side.

The X-axis sensor 10E and the Y-axis sensor 11E are disposed adjacent toeach other at an interval. The Z-axis sensors 12E are disposed tosurround the X-axis sensor 10E and the Y-axis sensor 11E, respectively.

In the present preferred embodiment, the Y-axis sensor 11E has anarrangement substantially similar to an arrangement obtained by rotating90 degrees the X-axis sensor 10E in a plan view. Therefore, hereinafter,instead of a detailed description of the arrangement of the Y-axissensor 11E, in the description of the portions of the X-axis sensor 10E,portions of the Y-axis sensor corresponding to the portions of theX-axis sensor are also described with parentheses.

Between the X-axis sensor 10E and the Z-axis sensor 12E and between theY-axis sensor 11E and the Z-axis sensor 12E, support portions 25E forsupporting these in a floating state are formed.

The support portions 25E have a lamination structure of the basesubstrate 7E, the base insulating layer 21E, and the polysilicon layer22E, and integrally include straight portions 26E and annular portions27E.

The straight portions 26E of the support portions 25E extend across theZ-axis sensors 12E from one side walls 28E of the lamination structurethat form the side surfaces partitioning the cavity 23E from the lateralsides toward the X-axis sensor 10E and the Y-axis sensor 11E. Theannular portions 27E of the support portions 25E surround the X-axissensor 10E and the Y-axis sensor 11E.

The X-axis sensor 10E and the Y-axis sensor 11E are disposed inside theannular portions 27E, and both ends of the sensors are supported at twopoints opposing each other on the inner walls of the annular portions27E. Both ends of the Z-axis sensors 12E are supported on both sidewalls of the straight portions 26E.

The X-axis sensor 10E (Y-axis sensor 11E) has an X fixed electrode 31E(Y fixed electrode 51E) and an X movable electrode 32E (Y movableelectrode 52E) formed to have the same thickness.

The X fixed electrode 31E (Y fixed electrode 51E) is fixed to thesupport portion 25E provided inside the cavity 23E.

The X fixed electrode 31E (Y fixed electrode 51E) includes a first baseportion 33E (first base portion 53E of the Y fixed electrode 51E) havinga quadrilateral annular shape in a plan view and fixed to the supportportion 25E, and a plurality of pairs of first comb tooth portions 34E(first comb tooth portions 54E of the Y fixed electrode 51E) alignedlike comb teeth at even intervals along the inner wall of the first baseportion 33E.

The first base portion 33E of the X fixed electrode 31E has atruss-shaped framed structure including straight main frames extendingparallel to each other and reinforcing frames combined with the mainframes so that a triangular space is repeatedly formed along the mainframes.

As the first comb tooth portions 34E of the X fixed electrode 31E, twoelectrode portions that have base end portions connected to the firstbase portion 33E and tip end portions thereof straight in a plan viewand opposed to each other are paired, and a plurality of the pairs areprovided at even intervals. Each first comb tooth portion 34E has aframed structure having a ladder-like shape in a plan view includingstraight main frames extending parallel to each other and a plurality oftraverse frames laid across the main frames.

The X movable electrode 32E (Y movable electrode 52E) is held to becapable of oscillating with respect to the X fixed electrode 31E.

The X movable electrode 32E (Y movable electrode 52E) includes a secondbase portion 35E (second base portion 55E of the Y movable electrode52E) and second comb tooth portions 36E (second comb tooth portions 56Eof the Y movable electrode 52E).

The second base portion 35E of the X movable electrode 32E is formed ofa plurality (six in the present preferred embodiment) of straight framesextending parallel to each other along a direction across the first combtooth portions 34E of the X fixed electrode 31E. Both ends of the secondbase portion 35E are connected to beam portions 37E (beam portions 57Eof the Y-axis sensor 11E) capable of expanding and contracting along adirection across the first comb tooth portions 34E.

Two beam portions 37E are provided on each of the ends of the secondbase portion 35E of the X movable electrode 32E.

The second comb tooth portions 36E of the X movable electrode 32E extendto both sides from the second base portion 35E toward the portionsbetween the first comb tooth portions 34E adjacent to each other of theX fixed electrode 31E, and are aligned like comb teeth to engage withthe first comb tooth portions 34E of the X fixed electrode 31E withoutcontact. Each second comb tooth portion 36E has a framed structurehaving a ladder-like shape in a plan view including straight main framesextending parallel to each other across the frames of the second baseportion 35E and a plurality of traverse frames laid across the mainframes.

In the X movable electrode 32E, on lines halving the second comb toothportions 36E along a direction orthogonal to the oscillation directionUx, insulating layers 38E across the traverse frames are embedded fromthe surface of the polysilicon layer 22E to the base insulating layer21E.

The insulating layers 38E are made of SiO₂ (silicon oxide), and areformed integrally with the base insulating layer 21E. The second combtooth portions 36E are insulated and separated into two of one side andthe other side along the oscillation direction Ux by the insulatinglayers 38E. Accordingly, the separated second comb tooth portions 36E ofthe X movable electrode 32E function as independent electrodes in the Xmovable electrode 32E.

On the polysilicon layer 22E, a first insulating film 42E and a secondinsulating film 43E made of SiO₂ are laminated in order. On the secondinsulating film 43E, an X first drive/detection wiring 39E (Y firstdrive/detection wiring 59E) and an X second drive/detection wiring 40E(Y second drive/detection wiring 60E) are formed.

The X first drive/detection wiring 39E supplies a drive voltage to oneside (in the present preferred embodiment, the left side on the papersurface of FIG. 35) of each second comb tooth portion 36E insulated andseparated into two, and detects a change in voltage accompanying achange in capacitance from the second comb tooth portion 36E.

The X second drive/detection wiring 40E supplies a drive voltage to theother side (in the present preferred embodiment, the right side on thepaper surface of FIG. 35) of each second comb tooth portion 36Einsulated and separated into two, and detects a change in voltageaccompanying a change in capacitance from the second comb tooth portion36E.

The first drive/detection wiring 39E and the X second drive/detectionwiring 40E are made of Al (aluminum) in the present preferredembodiment. The X first drive/detection wiring 39E and the X seconddrive/detection wiring 40E are electrically connected to the second combtooth portions 36E by penetrating through the first insulating film 42Eand the second insulating film 43E.

The X first drive/detection wiring 39E and the X second drive/detectionwiring 40E are led onto the support portion 25E via the beam portions37E of the X movable electrode 32E and the first base portion 33E of theX fixed electrode 31E, and partially exposed as electrode pads 9E.

The X first drive/detection wiring 39E and the X second drive/detectionwiring 40E use the beam portions 37E themselves formed of portions ofthe conductive polysilicon layer 22E as current paths in sectionspassing through the beam portions 37E of the X movable electrode 32E,respectively. Al wirings may not be provided on the beam portion 37E, sothat the expandability of the beam portions 37E can be maintained.

To the support portion 25E, an X third drive/detection wiring 41E thatdetects a change in voltage accompanying a change in capacitance fromthe first comb tooth portions 34E of the X fixed electrode 31E is led.The X third drive/detection wiring 41E is also partially exposed as anelectrode pad 9E (not shown) in the same manner as other wirings 39E and40E.

The upper surfaces and side surfaces of the X fixed electrode 31E andthe X movable electrode 32E are coated by the protective thin film 44Emade of SiO₂ so that the first insulating film 42E and the secondinsulating film 43E are covered.

On the polysilicon layer 22E, at portions except for the cavity 23E, athird insulating film 45E, a fourth insulating film 46E, a fifthinsulating film 47E, and a surface protective film 48E are laminated inorder on the second insulating film 43E.

In the X-axis sensor 10E structured as described above, via the X firstto X third drive/detection wirings 39E to 41E, drive voltages with thesame polarity and drive voltages with different polarities arealternately applied between the X fixed electrode 31E and the X movableelectrode 32E. Accordingly, coulomb repulsive and attractive forces arealternately generated between the first comb tooth portions 34E of the Xfixed electrode 31E and the second comb tooth portions 36E of the Xmovable electrode 32E.

As a result, the comb-tooth-like X movable electrode 32E oscillatessimilarly to the left and right along the X axis direction with respectto the comb-tooth-like X fixed electrode 31E (oscillation Ux).

In this state, when the X movable electrode 32E rotates around the Yaxis as a central axis, a coriolis force Fz is generated in the Z axisdirection. This coriolis force Fz changes the opposing area and/ordistance between the first comb tooth portions 34E of the X fixedelectrode 31E and the second comb tooth portions 36E of the X movableelectrode 32E adjacent to each other.

Then, by detecting a change in capacitance between the X movableelectrode 32E and the X fixed electrode 31E caused by the change inopposing area and/or distance, the angular velocity ωy around the Y axisis detected.

In the present preferred embodiment, the angular velocity ωy around theY axis is obtained by calculating a difference between detection valuesof the one side and the other side, respectively, electrode portionsinsulated and separated from each other of the X movable electrode 32E.

In the Y-axis sensor 11E, via the Y first to Y third drive/detectionwirings 59E to 61E, drive voltages with the same polarity and drivevoltages with different polarities are alternately applied between the Yfixed electrode 51E and the Y movable electrode 52E. Accordingly,coulomb repulsive and attractive forces are alternately generatedbetween the first comb tooth portions 54E of the Y fixed electrode 51Eand the second comb tooth portions 56E of the Y movable electrode 52E.

As a result, the comb-tooth-like Y movable electrode 52E oscillatessimilarly to the left and right along the Y-axis direction with respectto the comb-tooth-like Y fixed electrode 51E (oscillation Uy).

In this state, when the Y movable electrode 52E rotates around the Yaxis as a central axis, a coriolis force Fx is generated in the X-axisdirection. This coriolis force Fx changes the opposing area and/ordistance between the first comb tooth portions 54E of the Y fixedelectrode 51E and the second comb tooth portions 56E of the Y movableelectrode 52E adjacent to each other.

Then, by detecting a change in capacitance between the Y movableelectrode 52E and the Y fixed electrode 51E caused by the change inopposing area and/or distance, the angular velocity ωz around the Z axisis detected.

<Arrangement of Z-Axis Sensor>

Next, an arrangement of the Z-axis sensors will be described withreference to FIG. 34, FIG. 37, and FIG. 38.

FIG. 37 is a plan view of a principal portion of the Z-axis sensor ofFIG. 34. FIG. 38 is a sectional view of the principal portion of theZ-axis sensor shown in FIG. 34, illustrating a section taken along thecutting plane I-I in FIG. 37.

The Z-axis sensors 12E are disposed to surround the X-axis sensor 10Eand the Y-axis sensor 11E, respectively, directly above the cavity 23Eas described above.

Each Z-axis sensor 12E includes a Z fixed electrode 71E and a Z movableelectrode 72E formed to have the same thickness and the same width. InFIG. 37 and FIG. 38, the thickness and width of the Z fixed electrode71E are thickness T₁ and width W₁, respectively, and the thickness andwidth of the Z movable electrode 72E are thickness T₂ and width W₂,respectively.

The Z fixed electrode 71E is fixed to the support portion 25E (straightportion 26E) provided inside the cavity 23E.

The Z movable electrode 72E is held to be capable of oscillating withrespect to the Z fixed electrode 71E.

In the present preferred embodiment, in one Z-axis sensor 12E of the twoZ-axis sensors 12E, the Z movable electrode 72E is disposed to surroundthe annular portion 27E, and the Z fixed electrode 71E is disposed tosurround this Z movable electrode 72E.

In the other Z-axis sensor 12E, the Z fixed electrode 71E is disposed tosurround the annular portion 27E, and the Z movable electrode 72E isdisposed to surround this Z fixed electrode 71E.

In each Z-axis sensor 12E, the Z fixed electrode 71E includes a firstbase portion 73E and a plurality of first comb tooth portions 74E.

The first base portion 73E of the Z fixed electrode 71E is formed tohave a quadrilateral annular shape in a plan view fixed to the supportportion 25E. The first base portion 73E has a truss-shaped framedstructure including straight main frames extending parallel to eachother and reinforcing frames combined with the main frames so that atriangular space is repeatedly formed along the main frames.

In the first base portion 73E, on both sides of the portion (opposedportion 75E) opposed to the tip end portion 82E (described later) ofeach second comb tooth portion 79E, insulating layers 76E across themain frame of the truss structure in the width direction are embeddedfrom the surface of the polysilicon layer 22E to the cavity 23E.

The insulating layers 76E are made of SiO₂, and are formed integrallywith the base insulating layer 21E. Accordingly, the opposed portion 75Esurrounded by the insulating layers 76E and the triangular space of thetruss structure is insulated from other portions of the first baseportion 73E of the Z fixed electrode 71E.

The first comb tooth portions 74E of the Z fixed electrode 71E arealigned like comb teeth at even intervals along the inner wall of thefirst base portion 73E on the portion on the side opposite to thestraight portion 26E with respect to the X-axis sensor 10E (Y-axissensor 11E) on the first base portion 73E.

The first comb tooth portions 74E have base end portions connected tothe first base portion 73E of the Z fixed electrode 71E and tip endportions extending toward the Z movable electrode 72E. In portions closeto the base end portions of the first comb tooth portions 74E,insulating layers 77E across the first comb tooth portions 74E in thewidth direction are embedded from the surface of the polysilicon layer22E to the cavity 23E.

The insulating layers 77E are made of SiO₂, and formed integrally withthe base insulating layer 21E. Each first comb tooth portion 74E isinsulated from other portions of the Z fixed electrode 71E by theinsulating layer 77E.

In each Z-axis sensor 12E, the Z movable electrode 72E includes a secondbase portion 78E and second comb tooth portions 79E.

The second base portion 78E of the Z movable electrode 72E is formed tohave a quadrilateral annular shape in a plan view. The second baseportion 78E has a truss-shaped framed structure including straight mainframes extending parallel to each other and reinforcing frames combinedwith the main frames so that a triangular space is repeatedly formedalong the main frames.

The second base portion 78E of the framed structure has sections inwhich the reinforcing frames are omitted at portions on the sideopposite to the disposition of the second comb tooth portions 79E. Themain frames in these omitted sections function as beam portions 80E forenabling the Z movable electrode 72E to move up and down.

The second comb tooth portions 79E of the Z movable electrode 72E extendfrom the second base portion 78E toward the portions between the firstcomb tooth portions 74E adjacent to each other of the Z fixed electrode71E, and are aligned like comb teeth that engage with the first combtooth portions 74E without contact.

The second comb tooth portions 79E have base end portions 81E connectedto the second base portion 78E of the Z movable electrode 72E and tipend portions 82E extending toward the portions between the first combtooth portions 74E of the Z fixed electrode 71E.

In portions close to the tip end portions 82E of the second comb toothportions 79E, insulating layers 84E across the second comb toothportions 79E in the width direction are embedded from the surface of thepolysilicon layer 22E to the cavity 23E. In portions close to the baseend portions 81E of the second comb tooth portions 79E, insulatinglayers 85E across the second comb tooth portions 79E in the widthdirection are embedded from the surface of the polysilicon layer 22E tothe cavity 23E.

The insulating layers 84E and 85E are made of SiO₂, and are formedintegrally with the base insulating layer 21E. By the insulating layers84E and 85E, each second comb tooth portion 79E has three portions (thetip end portion 82E, the base end portion 81E, and an intermediateportion 83E between the tip end portion 82E and the base end portion81E) insulated from other portions.

On the polysilicon layer 22E, as described above, a first insulatingfilm 42E and a second insulating film 43E made of SiO₂ are laminated inorder. On the second insulating film 43E, a Z first detection wiring86E, a Z first drive wiring 87E, a Z second detection wiring 88E, and aZ second drive wiring 89E are formed.

The Z first detection wiring 86E and the Z second detection wiring 88Eare connected, respectively, to the first comb tooth portions 74E of theZ fixed electrode 71E and the intermediate portions 83E of the Z movableelectrode 72E adjacent to each other. Specifically, in the Z-axis sensor12E, the first comb tooth portions 74E of the Z fixed electrode 71E andthe intermediate portions 83E of the Z movable electrode 72E are opposedto each other at an electrode-to-electrode distance d, and constituteelectrodes of a capacitor (detector) when a fixed voltage is appliedtherebetween and the capacitance changes according to a change in theelectrode-to-electrode distance d and/or opposing area.

In detail, the Z first detection wiring 86E is formed along the firstbase portion 73E, and includes Al wirings branched toward the tip endportions of the first comb tooth portions 74E across the insulatinglayers 77E of the first comb tooth portions 74E.

The branched Al wirings are electrically connected to the tip end sidesrelative to the insulating layers 77E of the first comb tooth portions74E by penetrating through the first insulating film 42E and the secondinsulating film 43E.

As shown in FIG. 34, the Z first detection wiring 86E is led onto thesupport portion 25E via the first base portion 73E, and partiallyexposed as an electrode pad 9E.

The Z second detection wiring 88E detects a change in voltageaccompanying a change in capacitance from the second comb tooth portions79E of the Z movable electrode 72E. The Z second detection wiring 88E isformed along the second base portion 78E, and includes Al wiringsbranched toward the intermediate portions 83E across the insulatinglayers 85E close to the base end portions 81E of the second comb toothportions 79E.

The branched Al wirings are electrically connected to the intermediateportions 83E of the second comb tooth portions 79E by penetratingthrough the first insulating film 42E and the second insulating film43E.

As shown in FIG. 34, the Z second detection wiring 88E is led onto thesupport portion 25E via the second base portion 78E of the Z movableelectrode 72E, and partially exposed as an electrode pad 9E.

The Z first drive wiring 87E and the Z second drive wiring 89E areconnected, respectively, to the opposed portions 75E and the tip endportions 82E that face each other in the direction orthogonal to theopposing direction of the electrodes constituting a capacitor.Specifically, in the Z-axis sensor 12E, the opposed portions 75E of theZ fixed electrode 71E and the tip end portions 82E of the Z movableelectrode 72E opposed to each other at an interval constitute driveportions between which drive voltages are applied to oscillate the Zmovable electrode 72E by coulomb forces generated by changes in thedrive voltages.

In detail, the Z first drive wiring 87E supplies a drive voltage to theopposed portions 75E of the Z fixed electrode 71E. The Z first drivewiring 87E includes Al wirings across both sides of the insulatinglayers 76E by using the surface of the second insulating film 43E. The Zfirst drive wiring 87E is electrically connected to the opposed portions75E and portions except for the opposed portions 75E of the first baseportion 73E by penetrating through the first insulating film 42E and thesecond insulating film 43E. The portion except for the Al wirings of theZ first drive wiring 87E is formed by using the first base portion 73Eformed of the conductive polysilicon layer 22E.

As shown in FIG. 34, the Z first drive wiring 87E is led onto thesupport portion 25E and partially exposed as an electrode pad 9E.

The Z second drive wiring 89E supplies a drive voltage to the tip endportions 82E of the Z movable electrode 72E. The Z second drive wiring89E includes Al wirings laid across the tip end portions 82E and thebase end portions 81E of the second comb tooth portions 79E by using thesurface of the second insulating film 43E. The Z second drive wiring 89Eis electrically connected to the tip end portions 82E and the base endportions 81E by penetrating through the first insulating film 42E andthe second insulating film 43E. The portion except for the Al wirings ofthe Z second drive wiring 89E is formed by using the second base portion78E formed of the conductive polysilicon layer 22E.

As shown in FIG. 34, the Z second drive wiring 89E is led onto thesupport portion 25E, and partially exposed as an electrode pad 9E.

The upper surfaces and the side surfaces of the Z fixed electrode 71Eand the Z movable electrode 72E are coated by a protective thin film 44Emade of SiO₂ so that the first insulating film 42E and the secondinsulating film 43E are covered.

In the Z-axis sensor 12E structured as described above, drive voltageswith the same polarity and drive voltages with different polarities arealternately applied between the opposed portions 75E of the Z fixedelectrode 71E and the tip end portions 82E of the Z movable electrode72E via the Z first drive wiring 87E and the Z second drive wiring 89E.Accordingly, coulomb repulsive and attractive forces are alternatelygenerated between the opposed portions 75E and the tip end portions 82E.

As a result, the comb-tooth-like Z movable electrode 72E oscillates upand down like a pendulum similarly around the comb-tooth-like Z fixedelectrode 71E as a center of oscillation along the Z-axis direction withrespect to the Z fixed electrode 71E (oscillation Uz).

In this state, when the Z movable electrode 72E rotates around the Xaxis as a central axis, a coriolis force Fy is generated in the Y-axisdirection. This coriolis force Fy changes the opposing area and/orelectrode-to-electrode distance d between the first comb tooth portions74E and the intermediate portions 83E of the second comb tooth portions79E adjacent to each other.

Then, by detecting a change in capacitance C between the Z movableelectrode 72E and the Z fixed electrode 71E caused by the change inopposing area and/or electrode-to-electrode distanced, the angularvelocity ωx around the X axis is detected.

In the present preferred embodiment, the angular velocity ωx around theX axis is obtained by calculating a difference between a detection valueof the Z-axis sensor 12E surrounding the X-axis sensor 10E and adetection value of the Z-axis sensor 12E surrounding the Y-axis sensor11E.

For example, as shown in FIG. 34, the difference is obtained by makingthe position relationship between the fixed electrode and the movableelectrode of the Z-axis sensor 12E surrounding the X-axis sensor 10Eopposite to the position relationship between the fixed electrode andthe movable electrode of the Z-axis sensor 12E surrounding the Y-axissensor 11E. Accordingly, the manner of oscillation of the Z movableelectrode 72E differs between the pair of Z-axis sensors 12E, so thatthe difference occurs.

<Method for Manufacturing Angular Velocity Sensor>

Next, with reference to FIG. 39A to FIG. 39K, the manufacturing processof the above-described angular velocity sensor will be described inorder of steps. In this paragraph, only the manufacturing process of theZ-axis sensors is shown in the drawings, and the description of themanufacturing processes of the X-axis sensor and the Y-axis sensor areomitted, however, the manufacturing processes of the X-axis sensor andthe Y-axis sensor are performed in the same manner as in themanufacturing process of the Z-axis sensors in parallel to themanufacturing process of the Z-axis sensors.

FIG. 39A to FIG. 39K are schematic sectional views showing parts of themanufacturing process of the Z-axis sensors shown in FIG. 34 in order ofsteps, illustrating a section taken along the cutting plane at the sameposition as in FIG. 38.

To manufacture the Z-axis sensors 12E, the surface of the base substrate7E made of conductive silicon is thermally oxidized (for example,temperature: 1000° C. to 1200° C.). Accordingly, a mask (not shown) madeof SiO₂ is formed on the surface of the base substrate 7E. Next, by aknown patterning technique, the mask is patterned, and openings areformed at portions covering regions other than the regions in which theinsulating layers 76E, 77E, 84E and 85E should be formed.

Next, by anisotropic deep RIE (Reactive Ion Etching) using this mask asa hard mask, specifically, by a Bosch process, trenches (for example,depth: approximately 10 μm) are selectively formed in the base substrate7E. In the Bosch process, a step of etching the base substrate 7E byusing SF₆ (sulfur hexafluoride) and a step of forming a protective filmon the etched surfaces by using C₄F₈ (perfluorocyclobutane) arealternately repeated. Accordingly, the base substrate 7E can be etchedat a high aspect ratio, however, a wavy irregularity called scallop isformed on the etched surfaces (inner peripheral surfaces of thetrenches).

Accordingly, as shown in FIG. 39A, the left columnar portions where thetrenches were not formed of the base substrate 7E are formed as columnarportions 29E having the same shapes as the insulating layers 76E, 77E,84E, and 85E, and a plate-shaped base portion 30E that integrallysupports the bottom portions of the columnar portions 29E is formedconcurrently.

Next, as shown in FIG. 39B, the columnar portions 29E and the baseportion 30E of the base substrate 7E are thermally oxidized (forexample, temperature: 1000° C. to 1200° C.) Accordingly, the entirecolumnar portions 29E and the surface layer portion of the base portion30E are altered into insulating films made of SiO₂. Among the alteredinsulating films, the columnar portions 29E become the insulating layers76E, 77E, 84E, and 85E and the surface layer portion of the base portion30E becomes the base insulating layer 21E, respectively.

Next, on the surfaces of the insulating layers 76E, 77E, 84E, and 85Eand the base insulating layer 21E, a seed film made of polysilicon isformed. Subsequently, from this seed film, polysilicon is epitaxiallygrown. This epitaxial growth is continued until the height of the grownpolysilicon layer 22E becomes higher than the top portions (only the topportion 49E of the insulating layer 85E is shown in FIG. 39C) of thecolumnar portions 29E altered into the insulating layers 76E, 77E, 84E,and 85E as shown in FIG. 39C.

Next, as shown in FIG. 39D, by applying CMP (Chemical MechanicalPolishing) to the surface of the polysilicon layer 22E, the surface ofthe polysilicon layer 22E is made flush with the top portions 49E of thecolumnar portions 29E (insulating layer 85E). The top portions 49E ofthe columnar portions 29E are exposed to the surface of the polysiliconlayer 22E.

Next, as shown in FIG. 39E, by a CVD method, the first insulating film42E made of SiO₂ is laminated on the polysilicon layer 22E.

Next, as shown in FIG. 39F, the second insulating film 43E is laminatedon the first insulating film 42E. Subsequently, the second insulatingfilm 43E and the first insulating film 42E are successively etched.Accordingly, contact holes are formed in the second insulating film 43Eand the first insulating film 42E. Subsequently, after contact plugsfilling the contact holes are formed, Al is deposited (for example, 7000Å) by sputtering on the second insulating film 43E, and the Aldeposition layer is patterned. Accordingly, wirings 86E to 89E areformed on the second insulating film 43E.

Next, as shown in FIG. 39G, by a CVD method, the third insulating film45E, the fourth insulating film 46E, the fifth insulating film 47E, andthe surface protective film 48E are laminated in order on the secondinsulating film 43E. Next, the third to fifth insulating films 45E to47E and the surface protective film 48E on the region in which therecess 20E should be formed of the base substrate 7E are removed byetching.

Next, as shown in FIG. 39H, a resist having openings in regions exceptfor the regions in which the Z fixed electrode 71E and the Z movableelectrode 72E should be formed is formed on the second insulating film43E. Subsequently, by anisotropic deep RIE using the resist as a mask,specifically, by a Bosch process, the polysilicon layer 22E and the baseinsulating layer 21E are dug in order. Accordingly, the laminationstructure of the base insulating layer 21E and the polysilicon layer 22Eis molded into the shapes of the Z fixed electrode 71E as a firstelectrode or a second electrode and the Z movable electrode 72E as afirst electrode or a second electrode, and between these, trenches 50Eare formed. To the bottom surfaces of the trenches 50E, the surface ofthe base substrate 7E is exposed.

Next, as shown in FIG. 39I, by thermal oxidization or by a PECVD method,on the entire surfaces of the Z fixed electrode 71E and the Z movableelectrode 72E and the entire inner surfaces of the trenches 50E (thatis, the side surfaces and bottom surfaces defining the trenches 50E), aprotective thin film 44E made of SiO₂ is formed.

Next, as shown in FIG. 39J, by etching back, the portions on the bottomsurfaces of the trenches 50E of the protective thin film 44E areremoved. Accordingly, the bottom surfaces of the trenches 50E areexposed.

Next, as shown in FIG. 39K, by anisotropic deep RIE using the surfaceprotective film 48E as a mask, the bottom surfaces of the trenches 50E(that is, the surface of the base substrate 7E) are further dug.Accordingly, in the bottom portions of the trenches 50E (the surfacelayer portion of the base substrate 7E), exposure spaces 58E to whichthe crystal face of the base substrate 7E is exposed are formed.

Subsequent to this anisotropic deep RIE, by isotropic RIE, reactive ionsand etching gas as etching media are supplied into the exposure spaces58E of the trenches 50E. Then, by action of the reactive ions, etc., thebase substrate 7E is etched in a direction parallel to the surface ofthe base substrate 7E while being etched in the thickness direction ofthe base substrate 7E from the exposure spaces 58E. Accordingly, allexposure spaces 58E adjacent to each other are integrated to form arecess 20E (cavity 23E) on the surface layer portion of the basesubstrate 7E, and directly above the recess 20E, the Z fixed electrode71E and the Z movable electrode 72E is in a floating state.

Through the above-described steps, the Z-axis sensors 12E shown in FIG.34 are obtained.

According to the method described above, the lowest portions of the Zfixed electrode 71E and the Z movable electrode 72E are formed of thebase insulating layer 21E made of SiO₂ having etching selectivity to Si.Further, the side surfaces of the Z fixed electrode 71E and the Zmovable electrode 72E are also covered by the protective thin film 44Emade of SiO₂.

Therefore, in the step of FIG. 39K, when reactive ions and etching gasare supplied into the exposure spaces 58E and the base substrate 7E isisotropically etched, even if the etching gas, etc., come into contactwith the Z fixed electrode 71E and the Z movable electrode 72E, the Zfixed electrode 71E and the Z movable electrode 72E can be preventedfrom being eroded by the etching gas. As a result, the variation in size(the thicknesses T₁ and T₂ and the width W₁ and W₂) of the Z fixedelectrode 71E and the Z movable electrode 72E can be reduced.

Therefore, in the Z-axis sensor 12E, the opposing area between the firstcomb tooth portions 74E and the intermediate portions 83E of the secondcomb tooth portions 79E according to the thicknesses T₁ and T₂ of the Zfixed electrode 71E and the Z movable electrode 72E, and theelectrode-to-electrode distance d according to the widths W₁ and W₂ ofthe Z fixed electrode 71E and the Z movable electrode 72E can bemaintained constantly. Therefore, a change in capacitance between the Zmovable electrode 72E and the Z fixed electrode 71E caused by a changein the opposing area and/or electrode-to-electrode distance d can beaccurately detected.

The variations in the widths W₁ and W₂ of the Z fixed electrode 71E andthe Z movable electrode 72E are small, so that the magnitudes of coulombrepulsive and attractive forces to be generated at the respectiveportions between the opposed portions 75E and the tip end portions 82Ecan be made substantially equal to each other among the respectiveportions. As a result, the Z movable electrode 72E can be driven asdesigned.

In the invention described in Patent Document 1, the plurality ofportions that should be electrically insulated in the Si substrate areisolated by isolation joints (isolation joints 160, 360 . . . ). Theseisolation joints are formed by forming trenches in a Si substrate andthermally oxidizing the inner walls (side walls and bottom walls) of thetrenches as shown in FIG. 6 a of Patent Document 1. When the inner wallsof the trenches are thermally oxidized, SiO₂ grows from the side wallsand the bottom walls toward the insides of the trenches, and SiO₂ grownfrom the walls are eventually integrated. By this integration, isolationjoints (612 in FIG. 6 a) embedded in the trenches are obtained. However,the isolation joints thus obtained are films formed by growing aplurality of SiO₂ inside trenches that were originally void andintegrating these, so that the strength of the films is not so high, andthis formation takes time (for example, the etching rate isapproximately 2 μm/h).

Therefore, in the present preferred embodiment, the shapes of theinsulating layers 76E, 77E, 84E, and 85E for insulating and separatingthe portions of the Z fixed electrode 71E and the Z movable electrode72E from other portions are formed as columnar portions 29E by etchingthe base substrate 7E whose crystal structure is neat (the step of FIG.39A). Next, the columnar portions 29E are altered into insulating filmsby thermal oxidization (the step of FIG. 39B). Next, a polysilicon layer22E is formed around the insulating films (the step from FIG. 39C toFIG. 39D), and the polysilicon layer 22E is etched into the shapes ofthe Z fixed electrode 71E and the Z movable electrode 72E (the step ofFIG. 39H). Specifically, the shapes of the insulating layers 76E, 77E,84E, and 85E are formed by etching the base substrate 7E, so that ascompared with the method for forming the isolation joints in PatentDocument 1, the insulating layers with higher strength can be formed ina shorter time (for example, the etching rate is approximately 5 μm to10 μm/min.).

As shown in FIG. 39C, after polysilicon is epitaxially grown so as tocompletely cover the insulating layers 76E, 77E, 84E and 85E, byapplying CMP to the grown polysilicon, the thickness of the polysiliconlayer 22E is adjusted. Therefore, as compared with the case where thethickness of the polysilicon layer 22E is adjusted by considering thegrowth time of polysilicon from the seed film, etc., the polysiliconlayer 22E having a thickness equal to the height of the insulating filmsformed by the columnar portions 29E can be easily formed. Accordingly,the first comb tooth portions 74E and the opposed portions 75E of the Zfixed electrode 71E and the base end portions 81E, the tip end portions82E, and the intermediate portions 83E of the Z movable electrode 72Ecan be reliably insulated from other portions of the polysilicon layer22E, respectively.

As shown in FIG. 39F, previous to the step of molding the polysiliconlayer 22E into the Z fixed electrode 71E and the Z movable electrode 72E(the step of FIG. 39H), wirings 86E to 89E are formed on the polysiliconlayer 22E. Before molding the electrodes 71E and 72E, the space on thepolysilicon layer 22E can be effectively used. Even if a slightdifference occurs between the actually formed pattern of the wirings 86Eto 89E and the designed specification formation pattern, by correctingthe molded pattern of the electrodes 71E and 72E by considering thedifference, a sensor as designed can be manufactured finally.

The description of the operation and effects of the X-axis sensor 10Eand the Y-axis sensor 11E is omitted, however, the same operation andeffects as those of the above-described Z-axis sensor 12E can beobtained with the X-axis sensor 10E and the Y-axis sensor 11E accordingto the present preferred embodiment by arranging these as shown in FIG.34 to FIG. 36.

The MEMS package 1E according to the present preferred embodimentincludes the X-axis sensor 10E, the Y-axis sensor 11E, and the Z-axissensors 12E, so that the MEMS package can accurately detect angularvelocities applied around three axes (X axis, Y axis, and Z axis)orthogonal to each other in a three-dimensional space.

The fifth preferred embodiment of the present invention is describedabove, however the present invention can also be carried out in otherembodiments.

For example, the MEMS package 1E may include an acceleration sensorinstead of or in addition to the angular velocity sensor 3E. Theacceleration sensor can be manufactured, for example, by omitting thedrive portions in the sensors 10E to 12E shown in FIG. 34 to FIG. 38.For example, as shown in FIG. 40, a Z-axis acceleration sensor 90E thatdetects acceleration applied in the Z-axis direction can be manufacturedby omitting the opposed portions 75E of the Z fixed electrode 71E andthe tip end portions 82E of the Z movable electrode 72E that function asdrive portions and the wirings 87E and 89E connected to these portionsin the Z-axis sensor 12E shown in FIG. 37.

In the Z-axis acceleration sensor 90E, the variation in size(thicknesses T₁ and T₂ and widths W₁ and W₂) of the Z fixed electrode71E and the Z movable electrode 72E can be reduced.

Therefore, in the Z-axis acceleration sensor 90E, the opposing areabetween the first comb tooth portions 74E and the intermediate portions83E of the second comb tooth portions 79E according to the thicknessesT₁ and T₂ of the Z fixed electrode 71E and the Z movable electrode 72E,and the electrode-to-electrode distance d according to the widths W₁ andW₂ of the Z fixed electrode 71E and the Z movable electrode 72E can bemaintained constantly. Therefore, a change in capacitance between the Zmovable electrode 72E and the Z fixed electrode 71E caused by a changein the opposing area and/or electrode-to-electrode distance d can beaccurately detected. As a result, based on the change in capacitance,acceleration can be accurately detected.

The material of the base insulating layer 21E is not limited to SiO₂,and may be other materials (for example, SiN, etc.) having etchingselectivity to Si.

Preferred embodiments of the present invention are described in detailabove, however these are only detailed examples used for clarifying thetechnical contents of the present invention, and the present inventionshould not be interpreted as being limited to these detailed examples,and the spirit and scope of the present invention are limited only bythe claims attached hereto.

The above-described features grasped from the disclosure of the first tofifth preferred embodiments described above may be combined with eachother even among different preferred embodiments. The componentsdescribed in the preferred embodiments may be combined within the scopeof the present invention.

What is claimed is:
 1. A capacitance type sensor comprising: asemiconductor substrate having a cavity inside by forming an upper walland a bottom wall, and having a surface portion forming the upper wallof the cavity and a back surface portion forming the bottom wall; and afirst electrode and a second electrode that are formed by processing thesurface portion of the semiconductor substrate and have comb-tooth-likeshapes to engage with each other at an interval, where a change incapacitance between the first electrode and the second electrode isdetected.
 2. The capacitance type sensor according to claim 1, whereinthe first electrode includes dielectric layers that have a predeterminedthickness from the surface or the back surface to a halfway point of thefirst electrode along the thickness direction orthogonal to the opposingdirection of the second electrode and have a predetermined width alongthe opposing direction, and conductive layers consisting of remainingportions except for the dielectric layers.
 3. The capacitance typesensor according to claim 1, wherein the dielectric layers are one-sidedto one end side in the width direction of the first electrode, and theconductive layer includes a first portion formed adjacently on the otherend side in the width direction to the dielectric layer, and a secondportion formed below the dielectric layer and having a width larger thanthat of the first portion.
 4. The capacitance type sensor according toclaim 1, wherein the dielectric layers are formed from one end to theother end in the width direction of the first electrode and have thesame width as that of the first electrode, and the first electrode has alamination structure including the dielectric layers and the conductivelayers formed below the dielectric layers.
 5. The capacitance typesensor according to claim 1, wherein the first electrode is a movableelectrode and the second electrode is a fixed electrode.
 6. Thecapacitance type sensor according to claim 1, wherein the firstelectrode is a fixed electrode and the second electrode is a movableelectrode.
 7. The capacitance type sensor according to claim 1, whereinthe semiconductor substrate is a conductive silicon substrate.
 8. Thecapacitance type sensor according to claim 2, wherein the conductivelayers are portions formed by using a portion of the semiconductorsubstrate.
 9. The capacitance type sensor according to claim 2, whereinthe dielectric layers are made of SiO₂.
 10. The capacitance type sensoraccording to claim 1, further comprising a first insulating layer thatis selectively embedded in the first electrode and insulate and separatea certain portion of the first electrode from other portion of the firstelectrode.
 11. The capacitance type sensor according to claim 10,wherein the first insulating layer is made of SiO₂.
 12. The capacitancetype sensor according to claim 1, further comprising a second insulatinglayer that is selectively embedded in the second electrode and insulateand separate a certain portion of the second electrode from otherportion of the second electrode.
 13. The capacitance type sensoraccording to claim 12, wherein the second insulating layer is made ofSiO₂.
 14. The capacitance type sensor according to claim 1, comprisingan acceleration sensor that detects acceleration applied to thecapacitance type sensor by detecting a change in capacitance between thefirst electrode and the second electrode.
 15. The capacitance typesensor according to claim 1, comprising an angular velocity sensor thatdrives the first electrode in directions approaching and away from thecavity and detects an angular velocity applied to the capacitance typesensor at the time of this driving by detecting a change in capacitancebetween the first electrode and the second electrode.